Glossary of interior dimensions

32 mm system

The European cabinet drilling grid: holes at 32 mm (1 1/4 in) centres, set 37 mm (1 7/16 in) in from the front edge. Hinges, shelf pins and runners all land on it, which is why carcass heights come in multiples of 32 mm.

3-4-5 check

The site test for a right angle: measure 3 units along one wall and 4 along the other, and the diagonal should be 5. Use 3, 4 and 5 m, or in imperial 6, 8 and 10 ft, since the longer triangle exposes a smaller error.

600 mm module

The European carcass grid of 300, 400, 500, 600, 800 and 1,000 mm widths at 600 mm depth. The nearest US sizes are 12, 15, 18, 24 and 30 in, and since 24 in is 610 mm the two systems drift 10 mm per unit along a run.

Accent lighting

The layer that lights objects rather than tasks or rooms. Usually 10 to 15% of a room's total lumens, at a contrast ratio of about 3:1 against the ambient level for interest and up to 10:1 for drama.

ADA

The Americans with Disabilities Act standards, written for public buildings but the reference most US homes borrow from. The core figures are a 32 in (815 mm) clear door width, a 36 in (915 mm) route and a 60 in (1,525 mm) turning circle.

Ambient lighting

The general light level in a room, carrying roughly 50 to 60% of the total lumens. Delivered best from two or more positions rather than a single ceiling source.

Anthropometrics

The measurement of the human body and its ranges of movement. The source of nearly every interior clearance: shoulder breadth about 18 in (46 cm), walking sweep about 24 in (61 cm), seated eye height 38 to 44 in (97 to 112 cm).

Anti-fatigue mat

A cushioned mat for standing work, 10 to 19 mm (3/8 to 3/4 in) thick with a bevelled edge under 6 mm (1/4 in) so it does not trip. Standard sizes are 20 x 32 in and 24 x 36 in (51 x 81 and 61 x 91 cm).

Anti-tip restraint

The strap or bracket fixing a chest, bookcase or television to a stud. Fit one to any case over 27 in (69 cm) tall; US furniture stability testing hangs a 50 lb (22 kg) load on an open drawer to see whether the unit goes over.

Approved Document M

The England and Wales building regulations guidance on access and use. Its domestic figures include a 775 mm (30.5 in) clear door width, a 900 mm (35 in) corridor and switches and sockets between 450 and 1,200 mm (18 and 47 in).

Apron

The rail beneath a tabletop. It sets knee clearance: a table needs 24 to 26 in (61 to 66 cm) from the floor to the underside of the apron.

Architrave

The moulding covering the joint between a door frame and the wall, 60 to 100 mm (2 1/2 to 4 in) wide in the UK and 57 to 89 mm (2 1/4 to 3 1/2 in) in the US, held back from the frame edge by a reveal of 5 to 10 mm (1/4 to 3/8 in).

Arm height

Floor to the top of a sofa or chair arm, 24 to 27 in (61 to 69 cm) on most upholstery. It governs the side table beside it, which should land within 2 in (5 cm) of the same height to be useful for a drink.

AS 1428

The Australian design for access standard. It calls for a clear door width of 850 mm (33.5 in), a continuous accessible path of 1,000 mm (39 in) and a circulation space of 1,540 x 2,070 mm (61 x 81 in) for a 180 degree turn.

Back box

The recessed box behind a socket or switch. UK boxes come 25, 35 and 47 mm (1, 1 3/8 and 1 7/8 in) deep, and a 47 mm box will not fit a 40 mm (1 5/8 in) service void, so a shallower dry lining box is used instead.

Backrest angle

The angle between seat and back: 90 to 100 degrees for typing, 100 to 110 for reading, 110 to 130 for lounging. Every 10 degrees of recline adds roughly 2 in (5 cm) to the depth the chair needs behind it.

Backroom

The depth a sectional garage door needs behind the opening when fully open, equal to the door height plus about 18 in (46 cm). A 7 ft (2.13 m) door therefore wants roughly 8 ft 6 in (2.6 m) of unobstructed ceiling run.

Backset

The horizontal distance from the edge of a door to the centre of the handle or lock, normally 2 3/8 in (60 mm) or 2 3/4 in (70 mm) in the US and 45 mm or 57 mm in the UK. It decides whether your knuckles clear the frame.

Backsplash gap

The vertical distance from a kitchen worktop to the underside of the wall cabinets. Standard is 18 in (46 cm); 15 in (38 cm) is the practical minimum.

Baluster spacing

The gap between guard infill members, limited so that a 4 in (100 mm) sphere cannot pass in the US, and a 100 mm sphere under Approved Document K. On US stairs the triangle at the tread may pass a 6 in (150 mm) sphere.

Banquette

Fixed bench seating at a table. Seat height 17 to 18 in (43 to 46 cm), depth 18 to 20 in (46 to 51 cm), and it replaces the 36 in chair pull-out clearance with about 12 in (30 cm).

Barrier matting

The run of coarse matting that takes dirt and water off shoes before the floor finish begins. Allow at least 1.2 m (4 ft) of walking length outside and the same inside, rising to 3 m (10 ft) at a busy or exposed entrance.

Base cabinet

A floor-standing kitchen cabinet, 34.5 in (88 cm) high and 24 in (61 cm) deep in the US system, 720 mm high and 560 to 600 mm deep in the European. The worktop takes the finished height to 36 in (91 cm) or 900 mm.

Bass trap

Absorption set across a room corner to control low frequencies. Effective traps span 12 to 16 in (30 to 41 cm) across the corner and run floor to ceiling; anything under 100 mm (4 in) thick does little below 100 Hz.

Bathroom zones

The UK wiring zones around a bath or shower. Zone 0 is inside the bath itself, Zone 1 rises to 2.25 m (89 in) above the floor over it, and Zone 2 extends 600 mm (24 in) beyond Zone 1, each with its own protection requirement.

Beam angle

The cone of light a directional lamp produces. Narrow (15 to 25 degrees) for accent, wide (40 to 60 degrees) for general light. Beam diameter equals 2 x distance x tan(angle / 2).

Belfast sink

A deep fireclay utility basin, 600 x 455 x 255 mm (24 x 18 x 10 in) in the common size. Set the rim at 900 mm (36 in) and allow 250 mm (10 in) from basin base to spout so a bucket will fit under the tap.

Bend radius

The tightest curve a cable takes without damage, given as a multiple of its diameter. Cat 6 wants four times, about 25 mm (1 in), and coaxial ten times, about 70 mm (2 3/4 in), which is what sets the conduit and back box depth.

Bias lighting

A low-level light behind a screen that reduces eye strain in a dark room. Set it to roughly 10 per cent of the screen's peak brightness at 6500 K, in a strip about 4 in (10 cm) inside the edge of a 65 in (165 cm) panel.

Blackout side channel

The U-profile at each edge of a blackout blind that stops light leaking down the reveal. Channels are typically 25 to 30 mm (1 to 1 1/4 in) wide, and the blind is cut about 10 mm (3/8 in) narrower than the opening to run inside them.

Break

A curtain hem that rests about 1 in (2.5 cm) on the floor, producing a soft fold. Distinct from a float (1/2 in above), a kiss (touching) and a puddle (3 in or more).

Bumper plate

A rubber-coated Olympic plate 450 mm (17.7 in) in diameter whatever its weight, so a loaded bar always sits 225 mm (8.9 in) above the floor. That fixed height is why the pull position never changes as weight goes on.

Bunk guardrail

The rail on the open side of an upper bunk. US practice and the bunk bed safety standard put it at least 5 in (127 mm) above the mattress top, with any gap below the rail no wider than 3 1/2 in (89 mm).

Bunk headroom

The clear height between a bunk mattress top and whatever is above it. Allow 30 to 33 in (76 to 84 cm) so a child can sit up without ducking, which means a room ceiling of at least 8 ft (2.44 m) for a standard two-tier bunk.

Capture area

The plan area of a range hood canopy. Match the hob width at minimum and ideally add 76 mm (3 in) each side, with a canopy depth of 20 to 22 in (51 to 56 cm) so the front burners sit under it rather than in front.

Casement

A window hinged at the side and opening outward, the UK default. Opening leaves run 400 to 625 mm (16 to 25 in) wide because wider sashes catch the wind, and an escape light needs a clear area of 0.33 m2 (3.6 sq ft).

Ceiling airer

A ceiling-mounted drying rack on a pulley, commonly 1.2 to 1.8 m (4 to 6 ft) long with four to eight rails giving 5 to 11 m (16 to 36 ft) of line. Raised, it should leave 2 m (79 in) of headroom under the lowest rail.

Chaise return

The leg of a sectional running back into the room, 60 to 68 in (152 to 173 cm) deep on most models against a sofa depth of 36 to 40 in (91 to 102 cm). Measure it before the overall length, because it is what closes a walkway.

Changing table

A nappy changing surface set from the carer's elbow height, normally 36 to 43 in (91 to 109 cm) high and 20 to 24 in (51 to 61 cm) deep, with a guard 2 to 4 in (5 to 10 cm) on the open sides and supplies within a 20 in (51 cm) reach.

Clear floor space

The rectangle a wheelchair occupies while using a fixture, 30 x 48 in (760 x 1,220 mm) under the ADA and 800 x 1,300 mm (31 x 51 in) under Approved Document M. It may overlap knee space but not a door swing.

Clear width

The actual passable width of a doorway with the door open at 90 degrees, which is roughly the nominal door width minus 2 in (5 cm) for the stop and the slab. A 34 in door gives about 32 in (81 cm) of clear width, the accessible minimum.

Clearance

The empty floor space a fixture, appliance or piece of furniture needs to be used. Always measured from the face of the object, not the wall behind it.

Coefficient of utilisation (CU)

The fraction of a fixture's lumens that reach the working plane after the shade, walls and ceiling absorb their share. Typically 0.4 to 0.6 in a domestic room, and the term most consumer lumen calculators leave out.

Coffer

A recessed ceiling panel formed by crossing beams. Beams 150 to 300 mm (6 to 12 in) deep at 1.2 to 1.8 m (4 to 6 ft) centres suit a room of 2.7 m (9 ft) or more; under 2.4 m (8 ft) the drop is felt rather than seen.

Colour rendering index (CRI)

How faithfully a light source renders colour against a reference, on a 0 to 100 scale. Specify 90 or above at home, and check R9 (saturated red) is above 50, because skin and timber depend on it.

Console depth

The depth of a hall or sofa-back table, kept to 12 to 16 in (30 to 41 cm) so a 48 to 52 in (122 to 132 cm) hall still leaves a 36 in (91 cm) walkway. Behind a sofa it should match or sit just below the back height.

Consumer unit

The UK distribution board. Current practice, following Approved Document M, sets its switches between 1,350 and 1,450 mm (53 and 57 in) above the floor, with the door swing and a clear standing area kept free in front.

Cord cleat

The wall hook that holds a blind cord out of reach. The blind safety standards require that no loop hangs lower than 1.5 m (60 in) above the floor, and a cot should be kept at least 1 m (39 in) clear of any cord or chain.

Cornice

The moulding at the wall and ceiling junction, called crown in the US. Face sizes of 100 to 150 mm (4 to 6 in) suit a 2.4 m (8 ft) ceiling, rising to 150 to 230 mm (6 to 9 in) at 3 m (10 ft).

Correlated colour temperature (CCT)

The warmth or coolness of white light in kelvin. 2700 K is the domestic default, 3000 K suits kitchens and bathrooms, 3500 to 4000 K suits work and utility spaces.

Cot mattress gap

The tolerance between a cot or crib mattress and the frame. A US crib mattress is 28 x 52 in (71 x 132 cm) and a European cot bed mattress 70 x 140 cm (27.5 x 55 in); the gap on any side should stay under 25 mm (1 in).

Counter height

36 in (91 cm) in the US, 900 mm in Europe. Also the stool category that fits it, needing a seat height of 24 to 26 in (61 to 66 cm).

Counter-depth fridge

A refrigerator 24 to 25 in (61 to 64 cm) deep in the cabinet so it sits close to flush, against a standard depth of 30 to 36 in (76 to 91 cm). Doors and handles still project 2 to 4 in (5 to 10 cm) past the worktop edge.

Coverage rate

How far a material goes. Emulsion covers 10 to 12 m2 per litre (400 to 480 sq ft per US gallon) on a sealed wall, and a standard wallpaper roll of 10 m x 53 cm (33 ft x 21 in) covers about 5 m2 (54 sq ft).

Crossfall

The slope across a paved surface that sheds water, laid at 1 in 60 to 1 in 80 away from the house. That is 25 mm (1 in) of drop over 1.5 to 2 m (5 to 6.5 ft), and it is what stops a patio holding puddles.

Cubby

One person's share of a mudroom bank. An opening 15 to 18 in (38 to 46 cm) wide and 14 to 16 in (36 to 41 cm) deep, with the bench at 18 in (46 cm), a child hook at 42 in (107 cm) and a shelf above at 68 in (173 cm).

Cushion insert oversize

The rule that a feather insert is made 1 to 2 in (2.5 to 5 cm) larger than its cover, so a 20 in (51 cm) cover takes a 22 in (56 cm) insert. Without it the corners collapse and the cushion reads limp on a sofa.

Cutout

The hole in worktop or cabinetry an appliance drops into, always smaller than the appliance trim that covers it. A 30 in (762 mm) cooktop typically needs a cutout near 28 3/4 x 19 1/2 in (730 x 495 mm), taken from the model, not the class.

Dado rail

The UK chair rail, fixed at 900 to 1,000 mm (36 to 40 in) above the floor, or at one third of the ceiling height. A projection of 20 to 30 mm (3/4 to 1 1/4 in) is enough to stop a chair back marking the wall.

Datum line

A fixed reference height that every other dimension is measured from, usually a mark 1 m (39 in) above finished floor level. It stays true while floors and ceilings wander, and it keeps a run of joinery level in a poor room.

Deck joist spacing

The centres of deck framing, usually 16 in (406 mm) for boards laid square and 12 in (305 mm) for a 45 degree layout. Most composite boards demand 12 in centres regardless, which changes the joist count on a whole deck.

Deep seat cushion

Outdoor lounge upholstery, 5 to 6 in (13 to 15 cm) thick on the seat and 4 to 5 in (10 to 13 cm) on the back. It lifts a frame deck at 12 in (30 cm) to a finished seat height of 17 to 18 in (43 to 46 cm).

Deflection limit

The sag a shelf is allowed, conventionally the span divided by 180. On a 36 in (914 mm) shelf that is 5 mm (1/5 in), and beyond it the eye reads the shelf as bending even where the load is structurally safe.

Desire line

The route people actually take through a room, usually the shortest diagonal between two doors. Give it 36 in (91 cm) of width and keep furniture out of it, because a layout that blocks one is the layout that gets moved.

Dimension string

The chained run of measurements along the edge of a drawing, with an overall figure above it. Always check that the chain adds up to the overall; a 10 mm (3/8 in) discrepancy is the commonest error on a survey drawing.

Divan base

A UK upholstered bed base, 10 to 14 in (25 to 36 cm) high. With a mattress of 10 in (25 cm) it gives a sleep height of 24 to 26 in (61 to 66 cm), noticeably higher than a platform frame and easier to get out of.

Door leaf

The moving slab on its own, without frame or lining. US leaves are 80 in (2,032 mm) tall, 24 to 36 in (610 to 914 mm) wide and 1 3/8 in (35 mm) thick internally; the UK standard leaf is 1,981 x 762 x 35 mm (78 x 30 x 1 3/8 in).

Drawer runner

The slide a drawer rides on, sold in 50 mm (2 in) steps from 250 to 600 mm (10 to 24 in). It must be shorter than the internal depth of the carcass, so a 600 mm (24 in) deep cabinet usually takes a 500 or 550 mm runner.

Drop zone

The ledge just inside the front door where keys, post and a phone land. Trade practice is a shelf 4 to 6 in (10 to 15 cm) deep at 40 to 44 in (102 to 112 cm) above the floor, with a socket at ledge level for charging.

Egress

The route out of a building in an emergency, and the reason many minimum widths are code rather than preference. Egress routes in dwellings are generally 36 in (91 cm).

Elbow height

Floor to elbow when standing, roughly 0.63 of stature. A comfortable work surface sits 2 to 4 in (5 to 10 cm) below it, which puts a counter near 36 in (91 cm) for a user of 5 ft 6 in (168 cm) and higher for a taller one.

Euro hinge cup

The 35 mm (1 3/8 in) diameter bore, 11 to 13 mm (7/16 to 1/2 in) deep, that takes a concealed hinge, set 3 to 6 mm (1/8 to 1/4 in) in from the door edge. It is the most standardised dimension in cabinet making.

EVSE

Electric vehicle supply equipment, the wall charger itself. Mount the unit with its centre 36 to 48 in (91 to 122 cm) above the floor and plan the position around a cable of 16 to 25 ft (5 to 7.6 m) reaching a port anywhere on the car.

Expansion gap

The perimeter gap a floating floor needs to move, 10 to 15 mm (3/8 to 5/8 in) for engineered and laminate boards and more on runs over 8 m (26 ft). Skirting or beading covers it, and closing it is what makes a floor peak.

Extraction rate

The air a hood moves, in cubic feet per minute or cubic metres per hour, where 1 cfm equals 1.7 m3/h. Budget about 100 cfm (170 m3/h) per linear foot of hob, and more again over a wok burner or a griddle.

Eye height

Standing eye level averages about 5 ft 4 in (163 cm) for men and 5 ft (152 cm) for women, which is where the 57 in (145 cm) gallery centre line comes from. Seated at a dining table it drops to 44 to 48 in (112 to 122 cm).

Filler strip

The blank panel closing the gap between cabinetry and a wall or appliance. US practice uses fillers up to 3 in (76 mm) wide, and at least 1 1/2 in (38 mm) is needed at an inside corner so drawers clear the adjacent handles.

Finished floor level

FFL, the top of the final floor covering rather than the structural deck. A 22 mm (7/8 in) board with 15 mm (5/8 in) of tile and adhesive over it lifts the FFL by 37 mm (1 1/2 in), which is enough to stop a door.

Fire pit clearance

The distance an open fire keeps from anything that burns. Trade practice and most manufacturers ask for 10 ft (3 m) to a structure or overhang, with seating 24 to 36 in (61 to 91 cm) back from the rim of the bowl.

First reflection point

The spot on a wall, floor or ceiling where sound bounces once between speaker and listener, found by sliding a mirror along the surface. Treat it with a panel about 24 x 48 in (61 x 122 cm) and at least 50 mm (2 in) thick.

Flue terminal clearance

The distance a boiler flue outlet must keep from openings and boundaries. UK installation practice normally requires 300 mm (12 in) from a window or door and 600 mm (24 in) below a balcony or overhanging structure.

Foot-candle (fc)

One lumen per square foot of surface. The unit lighting recommendations are written in. 1 fc equals 10.76 lux.

Front-load washer

A horizontal-axis washing machine, 27 in (68.5 cm) wide in the US and 600 mm (23.6 in) in Europe, 24 to 34 in (61 to 86 cm) deep. Add 20 to 22 in (51 to 56 cm) for the open door and 4 to 6 in (10 to 15 cm) behind for hoses.

Fullness

The ratio of a curtain's flat fabric width to the width it covers. 1.5x is sparse, 2x is standard, 2.5 to 3x reads as luxurious. The single most common cause of disappointing curtains is a ratio near 1.1x.

Functional reach

The distance a person can reach forward and still grip something, about 24 to 30 in (61 to 76 cm) from the shoulder. It is why a worktop stops at 25 in (64 cm) deep and a wall cabinet at 13 in (33 cm).

Gang

One switch or socket position on a plate. A UK single gang plate is 86 x 86 mm (3.4 x 3.4 in) and a double 146 x 86 mm (5.7 x 3.4 in), so each extra gang adds roughly 60 mm (2 3/8 in) of wall width to the group.

Garage headroom

The height between the top of a garage door opening and the ceiling, needed for the door to roll back. A standard torsion setup wants 12 in (30 cm), a low-headroom kit about 4 1/2 in (114 mm), and a jackshaft opener around 6 in (15 cm).

Going

UK term for the horizontal depth of a stair tread, measured nosing to nosing. Minimum 220 mm for a private stair under Approved Document K. The US equivalent term is run.

Grab bar

A rail fixed 33 to 36 in (840 to 915 mm) above the floor, with a gap of 1 1/2 in (38 mm) to the wall and a diameter of 1 1/4 to 2 in (32 to 51 mm). It needs blocking able to take 250 lb (113 kg) of pull.

Guard height

The barrier at the edge of a deck, balcony or landing. The IRC requires 36 in (91 cm) at a dwelling, the IBC 42 in (107 cm), and Approved Document K asks for 1,100 mm (43 in) on a balcony above ground level.

Hard conversion

A genuine change of size to a round metric figure, so a 4 x 8 ft sheet is made at 1,200 x 2,400 mm rather than 1,219 x 2,438 mm. The 19 mm (3/4 in) lost per sheet is why mixed-system setting out drifts.

Hearth extension

The non-combustible floor area in front of a fireplace opening. Under IRC R1001.10 that is at least 16 in (41 cm) in front and 8 in (20 cm) to each side for openings under 6 sq ft, and 20 in and 12 in for larger openings.

Hook rail

A board of hooks fixed to an entry wall. Adult hooks sit at 60 to 68 in (152 to 173 cm), children's at 36 to 42 in (91 to 107 cm), spaced 8 to 12 in (20 to 30 cm) apart so a coat on one does not bury the next.

Illuminance

The amount of light landing on a surface, measured in foot-candles or lux. The quantity worth designing to, as opposed to the lumens a lamp emits.

Inside mount

A blind or shade fitted within the window reveal. Needs a minimum flat depth (about 2 in for a roller, 3 to 3.5 in for a roman) and always leaves a light gap of 1/4 to 1/2 in per side.

IP rating

Two digits for ingress protection, solids then water. IPX4 is splash-proof and the usual minimum for bathroom Zone 2, while IPX7 means immersion to 1 m (39 in) for 30 minutes, which is what a Zone 0 fitting must survive.

IRC

The International Residential Code, the model US code for one and two family homes. It is the source of the 36 in (915 mm) hallway, the 7 3/4 in (197 mm) maximum riser and the 6 ft 8 in (2,032 mm) stair headroom.

Ironing board

A board 12 to 18 in (30 to 46 cm) wide and 48 to 54 in (122 to 137 cm) long, adjustable between 28 and 38 in (71 and 97 cm). In use it claims about 25 sq ft (2.3 m2) of floor once the user is standing at it.

Jackshaft opener

A garage door motor mounted on the wall beside the torsion shaft instead of on the ceiling. It frees the whole ceiling for storage and needs only about 6 in (15 cm) of headroom and 8 in (20 cm) of side room to fit.

Kiss

A curtain hem that just touches the floor. The most tailored option and the least forgiving of an uneven floor.

Knee clearance

The open volume under a work surface. 24 to 27 in (61 to 69 cm) high and at least 20 in (51 cm) wide for a desk; the ADA figure for a seated user is 27 in high, 30 in wide and 11 to 25 in deep.

LAF and RAF

Left arm facing and right arm facing, the codes for sectional modules, read as you look at the piece. A LAF chaise 68 in (173 cm) deep cannot be swapped to the other end, so the code decides which way the room works.

Landing space

Kitchen term for uninterrupted worktop next to an appliance: 15 in (38 cm) beside the fridge handle side, 12 in on one side of a cooktop and 15 in on the other, 15 in beside or above a microwave.

Latch-side clearance

The wall space beside a door on the handle side, needed to pull it open from a wheelchair. The ADA asks for 18 in (455 mm) on a front approach to the pull side, and Approved Document M for 300 mm (12 in) at the leading edge.

Laundry pedestal

A drawer base under a front loader, 12 to 15 in (30 to 38 cm) high. It lifts the door opening to a comfortable 24 to 30 in (61 to 76 cm) and raises the machine top, so a worktop over the pair has to rise with it.

Lens shift

The optical offset that lets a projector sit above or below screen centre without keystoning, quoted as a percentage of image height. Sixty per cent of vertical shift on an image 50 in (127 cm) tall moves the lens 30 in (76 cm).

Lifting platform

The shock-absorbing deck for deadlifts and cleans, standard at 8 x 8 ft (2.44 x 2.44 m). It is usually two layers of 18 mm (3/4 in) ply with rubber on the drop zones and hardwood down the centre, adding 50 mm (2 in) to the floor.

Lippage

The height difference between two adjacent tiles. Trade tolerance is about 1 mm (1/32 in) on narrow joints, held with levelling clips on long formats. Anything over 2 mm (1/16 in) catches raking light and catches a toe.

Long hang

The wardrobe zone for coats and dresses, needing 60 to 70 in (152 to 178 cm) of clear height with the rod at 66 to 72 in (168 to 183 cm). Most coats need only 52 in (132 cm), so full-height long hang is often wasted space.

Lumen (lm)

Total light output of a source. A traditional 60 W incandescent lamp produces about 800 lm; a modern LED produces the same from 7 to 10 W.

Luminous efficacy

Lumens produced per watt consumed. An incandescent lamp manages 12 to 17 lm/W, a halogen about 20, and an LED 80 to 120 lm/W, which is why the same 800 lumen output moved from 60 W down to roughly 8 W.

Lux

One lumen per square metre. The metric illuminance unit. 100 lux is a dim room, 300 lux a working kitchen, 500 lux a desk.

Makeup air

Replacement air for a powerful extract fan. US codes call for a makeup supply once a hood exceeds 400 cfm (680 m3/h), normally a duct of 6 to 8 in (150 to 200 mm) with a motorised damper interlocked to the hood.

Matwell

A recess in the entry floor that holds barrier matting flush with the finished surface, normally 12 to 15 mm (1/2 to 5/8 in) deep. Size it to catch two full paces, about 1.2 m (48 in) of walking length, or it does nothing.

Movement joint

A deliberate break in a tiled field, needed every 8 to 10 m (26 to 33 ft) indoors, at internal corners and over any structural joint. Joints are 6 to 10 mm (1/4 to 3/8 in) wide and filled with silicone rather than grout.

Mullion

The vertical member dividing a window into separate lights, typically 50 to 100 mm (2 to 4 in) wide in timber and about 60 mm (2 1/4 in) in PVCu. The horizontal equivalent is a transom, and both cut into the glazed area.

Nationally Described Space Standard

The English standard for new home sizes. A single bedroom must be at least 7.5 m2 (81 sq ft) and 2.15 m (85 in) wide, a double 11.5 m2 (124 sq ft) and 2.75 m (108 in) wide, with 2.3 m (90.5 in) of floor to ceiling height.

Newel

The post anchoring a balustrade at the foot, turn and head of a stair. 90 x 90 mm (3 1/2 x 3 1/2 in) is the domestic standard, with the handrail meeting it 900 to 1,000 mm (36 to 39 in) above the pitch line.

Nominal size

The name a component is sold under rather than its measured dimension. A 2x4 is 1.5 x 3.5 in; a 32 in door gives about 30 in of clear width. Always plan to the measured figure.

Nosing

The projecting front edge of a stair tread, typically 3/4 to 1.25 in (19 to 32 mm). It adds to effective tread depth without adding to the total run.

Obstructed reach

The penalty for reaching over something. Under the ADA a forward reach over an obstruction 20 in (510 mm) deep drops the high reach from 48 to 44 in (1,220 to 1,120 mm), and a side reach over 24 in (610 mm) drops it to 46 in (1,170 mm).

Offset limit

The maximum stagger in a brick-bond tile layout. Long formats bow slightly in the middle, so manufacturers cap the offset at one third rather than one half on any tile over 380 mm (15 in) long.

Olympic barbell

The standard bar at 7 ft 2 in (2.2 m) long and 20 kg (44 lb), with 51 in (129 cm) between the collars. Its length is what sets the minimum usable width of a lifting area at about 8 ft (2.44 m) wall to wall.

Operating force

How hard a control may be to work. The ADA caps interior door opening force at 5 lbf (22 N) and Approved Document M at 30 N, and both require handles and taps that work with a closed fist, without grasping or twisting.

Out of square

The amount a room deviates from a right angle, typically 10 to 25 mm (3/8 to 1 in) over a 3 m (10 ft) wall. Check it by comparing diagonals; more than 25 mm and fitted furniture will need a scribe rather than a filler.

Outfeed space

The clear run a workpiece needs beyond a machine. A table saw ripping full sheets wants 8 ft (2.44 m) of outfeed and the same again as infeed, and a mitre saw wants 8 ft (2.44 m) each side of the blade for trim lengths.

Outside mount

A blind or shade fitted to the wall or casing above a window, overlapping it by 2 in (5 cm) each side and 3 to 4 in (8 to 10 cm) above. The only reliable way to get true blackout.

Overhang

The projection of a worktop past the cabinet below. 1 in (2.5 cm) at a standard run; 12 in (30 cm) for knees at a 36 in counter, 15 in (38 cm) at a 30 in table-height surface and 10 in (25 cm) at a 42 in bar.

Overhead rack

A ceiling-hung storage platform in a garage, commonly 4 x 8 ft (1.2 x 2.4 m) with an adjustable drop of 24 to 45 in (61 to 114 cm). Keep the loaded underside clear of the door track and no lower than 7 ft (2.13 m) over a walking route.

Panel-ready

An appliance built to take a cabinet door rather than a finished front. Panels are 19 mm (3/4 in) thick and follow the door module, with a reveal of 3 to 6 mm (1/8 to 1/4 in) around them to match the rest of the run.

Parking bay

A marked car space, 8.5 x 18 ft (2.6 x 5.5 m) in US practice and 2.4 x 4.8 m (7.9 x 15.7 ft) in UK guidance. Neither figure includes the space to open a door, which needs a further 30 in (76 cm) beside the car.

Pattern repeat

The vertical distance before a wallpaper or fabric design returns. A repeat of 52 cm (20 in) on a drop of 2.4 m (94 in) can waste most of a repeat per length, so drops are ordered in whole repeats rounded up.

Percentile

The share of a population a dimension serves. Size clearances to the 95th percentile male at about 6 ft 2 in (188 cm) and set reach heights to the 5th percentile female at about 5 ft (152 cm), so both ends are covered.

Pergola purlin

The upper slats crossing the rafters of a pergola. Spacing 50 mm (2 in) members at 100 to 150 mm (4 to 6 in) centres gives roughly half shade at midday, while 300 mm (12 in) centres give closer to a quarter.

Picture rail

A moulding fixed 300 to 450 mm (12 to 18 in) below the ceiling and often aligned with the door head at 2,032 mm (80 in). Pictures hang from it on cord, so the drop, not the fixing, sets the frame centre.

Pitch

The angle of a staircase. Approved Document K caps a private stair at 42 degrees; typical comfortable domestic pitch is 32 to 37 degrees.

Plinth block

The square block at the foot of a door architrave, made thicker and wider than both the casing and the skirting so the two can butt into it. Typically 25 mm (1 in) thick, 120 mm (4 3/4 in) wide and 200 mm (8 in) tall.

Pocket cassette

The steel and board cage a sliding door disappears into. It calls for a finished wall about 100 mm (4 in) thick and a length of twice the door width plus 20 to 50 mm (1 to 2 in) for the jamb and stop.

Popliteal height

The distance from floor to the underside of the knee when seated, 15 to 18 in (38 to 46 cm) across most adults. Seat heights are derived from it, which is why 17 to 18 in (43 to 46 cm) is the near-universal chair height.

Power rack

A four-post lifting frame with a footprint of about 48 x 48 in (122 x 122 cm) and a height of 84 to 93 in (213 to 236 cm). Allow 24 in (61 cm) behind for the pull-up swing and roughly 8 ft (2.44 m) of width for the bar.

Proxemics

Edward T. Hall's study of the distances people keep from each other. The source of the 4 to 12 ft (1.2 to 3.7 m) social distance band that sets conversational seating layouts.

Pull-out larder

A tall basket or shelf unit on full-extension runners, 300, 400 or 600 mm (12, 16 or 24 in) wide and up to 2 m (79 in) tall. It needs its full 560 mm (22 in) of depth as clear aisle in front before it will open.

Rack unit

The vertical module for equipment racks. One U is 1.75 in (44.45 mm) high in a frame 19 in (483 mm) wide. A 12U cabinet gives 21 in (533 mm) of usable height and wants 4 in (100 mm) of clear air behind for cables and heat.

Raised bed width

Set by arm reach rather than by timber lengths. Allow 4 ft (1.2 m) where both sides can be reached, 30 in (76 cm) against a wall, with 18 to 24 in (46 to 61 cm) of path between beds and 36 in (91 cm) where a barrow must pass.

Ramp gradient

The slope of an accessible ramp, capped at 1 in 12 by the ADA with a maximum run of 30 ft (9 m) between landings. Approved Document M eases longer runs to 1 in 15 or 1 in 20, and every landing is at least 1,500 mm (59 in) long.

Reach range

The band a seated or standing person can reach without straining. The accessible range is 15 to 48 in (38 to 122 cm) from the floor; comfortable standing reach ends around 72 to 78 in (183 to 198 cm).

Reach-in closet

A wardrobe you stand outside rather than in. Depth is 24 to 26 in (61 to 66 cm) because that is what a hanger on a rod needs, and beyond about 8 ft (2.4 m) of width the corners become unreachable through the doors.

Recessed dryer box

A wall box letting the vent elbow sit inside the stud bay, typically 21 x 8 in (53 x 20 cm) and 3 1/2 in (89 mm) deep. It recovers 3 to 4 in (8 to 10 cm) of the gap behind a dryer, which is often the difference in a laundry closet.

Rectified tile

A tile mechanically ground to an exact size after firing, allowing joints of 2 to 3 mm (1/16 to 1/8 in). Pressed tiles vary enough to need 3 to 5 mm (1/8 to 3/16 in), which is why joint width follows the tile, not taste.

Reveal

The depth of the window opening from the face of the wall to the glass. It determines whether an inside-mount blind is possible.

Rise

The vertical height of one stair step. The IRC caps it at 7.75 in (197 mm); Approved Document K caps it at 220 mm. Variation between risers on the same flight must stay within 3/8 in (10 mm).

Rough opening

The framed opening a door or window sits in, typically the unit size plus 2 in (5 cm) in width and 2.5 in (6 cm) in height for a door.

Rubber gym tile

Interlocking or square rubber flooring, 8 mm (5/16 in) for general use, 15 to 20 mm (5/8 to 3/4 in) under free weights and 30 to 40 mm (1 1/4 to 1 1/2 in) in a drop zone. The common tile is 1 x 1 m (39 x 39 in).

Run

US term for the horizontal depth of a stair tread, minimum 10 in (254 mm) under the IRC. Total run is the tread depth multiplied by the number of treads, and it is the figure that tells you how much floor a staircase eats.

Scale

The ratio a drawing is reduced by. Interiors are drawn at 1:50 for plans, 1:20 for detailed layouts and 1:5 for joinery, the rough imperial equivalents being 1/4 in and 1/2 in to the foot.

Screed

The levelling layer over a slab. Traditional sand and cement is 65 to 75 mm (2 1/2 to 3 in) thick, flowing anhydrite 40 to 50 mm (1 1/2 to 2 in), and either needs about 30 mm (1 1/4 in) of cover over underfloor heating pipes.

Scribe

The tapered cut that makes a fitted unit follow an out-of-square wall. Joiners leave a scribe allowance of 15 to 25 mm (5/8 to 1 in) on an end panel, because walls commonly wander 10 to 20 mm (3/8 to 3/4 in) over a 3 m (10 ft) run.

Seat depth

The cushion measured from the front edge to the face of the back cushion. 21 to 22 in (53 to 56 cm) suits upright sitting, 23 to 25 in (58 to 64 cm) lounging, and anything over 26 in (66 cm) needs a bolster or a tall user.

Seating riser

The stepped platform lifting a rear row in a home theatre, normally 8 to 12 in (20 to 30 cm) high with rows 60 to 72 in (152 to 183 cm) apart, so the rear viewer's eye clears the head in front by at least 4 in (100 mm).

Sectional door

A panelled garage door that lifts into horizontal tracks. Common US singles are 8 or 9 x 7 ft (2.44 or 2.74 x 2.13 m) and doubles 16 x 7 ft (4.88 x 2.13 m); the traditional UK single opening is 2,134 x 1,981 mm (84 x 78 in).

Setting out

Deciding where the first line goes before anything is fixed. Tiles are set out from the centre so that no perimeter cut falls below half a tile, or about 50 mm (2 in), and boards are set out to the sightline from the main door.

Shaver socket

An isolated low-power bathroom outlet. Keep it at least 600 mm (24 in) horizontally from a bath or shower edge so it sits outside Zone 2, typically at 1,100 to 1,200 mm (43 to 47 in) above the floor beside a mirror.

Short hang

Double hanging for shirts, jackets and folded trousers, with rods at 42 and 84 in (107 and 213 cm) and about 40 in (102 cm) of clear height under each. It doubles capacity within the same run of wardrobe width.

Sidelight

A fixed glazed panel beside a front door, commonly 12 or 14 in (305 or 356 mm) wide by the door height. A 36 in (914 mm) door with two of them takes the rough opening to about 60 or 64 in (1,524 or 1,626 mm).

Sightline

An uninterrupted line of view through a space. Preserving the longest diagonal sightline is the single most effective move in a small room.

Sit-stand range

The travel a height-adjustable desk must cover to serve a household, roughly 25 to 50 in (64 to 127 cm). A user of 5 ft 10 in (178 cm) stands at about 43 in (109 cm) and sits at about 29 in (74 cm).

Six-foot rule

The NEC requirement that no point along a wall is more than 6 ft (1.8 m) from a receptacle, which puts general outlets on 12 ft (3.7 m) centres. Over a kitchen counter the spacing tightens to 4 ft (1.2 m) centres.

Skirting

The UK term for baseboard. Run 120 to 170 mm (5 to 7 in) under a 2.4 m (8 ft) ceiling and 200 mm (8 in) or more under 3 m (10 ft). Thickness of 18 to 25 mm (3/4 to 1 in) must stay thinner than the architrave it butts into.

Slat spacing

The gap between cot or crib bars, capped at 2 3/8 in (60 mm) in the US and set between 45 and 65 mm (1 3/4 and 2 1/2 in) by EN 716, so a child's head cannot pass through and a limb cannot be trapped.

Slide-in range

A cooker made to sit between cabinets with its worktop lapping over them, typically 29 7/8 in (759 mm) wide for a 30 in (762 mm) opening. It has no back panel, so the wall behind must be finished as a backsplash.

Slimline dishwasher

A machine 450 mm (17.7 in) wide against the 600 mm (23.6 in) standard, holding about nine place settings rather than thirteen. It buys back 150 mm (6 in) of worktop, which is a drawer stack in a small kitchen.

Soft conversion

Restating an imperial size in metric without changing the product, so a 24 in cabinet is labelled 610 mm and a 4 x 8 ft sheet 1,219 x 2,438 mm. It looks metric and is not, which is the trap in a mixed specification.

Spacing criterion (SC)

A downlight's published ratio of spacing to mounting height above the working plane, typically 1.0 to 1.5. Multiply it by the mounting height to get the maximum spacing for even light.

Spring angle

The angle at which crown moulding leans off the wall, normally 38 or 45 degrees. A 45 degree profile with a face of 127 mm (5 in) gives an equal projection and drop of about 89 mm (3 1/2 in), which is what the ceiling sees.

Square metre

The metric area unit, equal to 10.764 sq ft. A room of 12 x 14 ft is 168 sq ft or 15.6 m2, and the common shorthand of dividing square feet by ten overstates the metric area by about 7 per cent when ordering.

Stack-back

The wall width a pair of curtains occupies when fully open. Roughly a third of the covered width for a pleated heading, which is why rods need to extend well past the window.

Stacking kit

The bracket that fixes a dryer above a washer. The stack stands 70 to 80 in (178 to 203 cm) tall and puts the dryer controls at 60 to 66 in (152 to 168 cm), which is the top of a comfortable reach for a user of 5 ft 4 in (163 cm).

Stile

The vertical outer member of a panelled door, usually 100 to 125 mm (4 to 5 in) wide, matched by a top rail of the same width and a bottom rail of 200 to 250 mm (8 to 10 in). Width trimming comes off the stiles, rarely more than 6 mm (1/4 in) a side.

Storage bench

The seat in an entry or mudroom, built at 17 to 18 in (43 to 46 cm) high and 15 to 18 in (38 to 46 cm) deep. Allow 24 in (61 cm) of length per person and keep 36 in (91 cm) of clear floor in front for tying laces.

Structural opening

The masonry or framed opening a UK window or door is built into, quoted before plaster. Allow about 10 mm (3/8 in) of packing each side and at the head so the frame can be levelled and packed square.

Superking

The largest standard UK bed, 180 x 200 cm (71 x 79 in). It is about 5 in (13 cm) narrower and 1 in (2.5 cm) shorter than a US king of 76 x 80 in (193 x 203 cm), so bedding does not cross between the two markets.

Task lighting

Light delivered close to the work: 25 to 30% of a room's lumens, at 70 to 80 foot-candles on a kitchen worktop or a desk.

Threshold ramp

The small wedge easing a doorway step. The ADA allows a threshold up to 13 mm (1/2 in) provided anything above 6 mm (1/4 in) is bevelled at 1 in 2, while UK accessible practice asks for an upstand no greater than 15 mm (5/8 in).

Throw ratio

A projector's throw distance divided by the image width. A ratio of 1.5 puts a 100 in (254 cm) wide image 150 in (381 cm) from the screen. Short throw is under 1.0 and ultra short throw under 0.4, which allows a cabinet-top position.

Toddler bed

An intermediate bed reusing the cot mattress, 28 x 52 in (71 x 132 cm) in the US or 70 x 140 cm (27.5 x 55 in) in Europe. The mattress top sits at 8 to 12 in (20 to 30 cm), with side rails about 5 in (13 cm) above it.

Toe kick / plinth

The recess at the base of a cabinet, 4 in (10 cm) high and 3 in (8 cm) deep as standard, which lets you stand close to the worktop without stubbing your toes.

Toilet rough-in

The distance from the finished wall to the centre of the soil outlet. US practice is 12 in (305 mm), with 10 and 14 in (254 and 356 mm) variants. UK pans use a horizontal outlet instead, at about 180 mm (7 in) above the floor.

Transfer space

The clear floor beside a toilet, bath or bed for moving across from a wheelchair. The ADA wants 60 in (1,525 mm) of width at a toilet, and Approved Document M guarantees it with a WC compartment of 1,500 x 2,200 mm (59 x 87 in).

Transition duct

The flexible length between a dryer and the rigid vent. The IRC limits it to 8 ft (2.44 m) and forbids it passing through a wall. The rigid duct itself is 4 in (100 mm) in diameter with a maximum developed length of 35 ft (10.7 m).

Transition strip

The profile joining two floor finishes at a doorway. The ADA allows a vertical lip of 6 mm (1/4 in), or up to 13 mm (1/2 in) if bevelled at 1 in 2; beyond that the change has to be ramped rather than covered.

Transom

The fixed light above a door or window, historically 12 to 18 in (30 to 46 cm) tall. It lifts the head of the opening from the 6 ft 8 in (2,032 mm) door datum towards 8 ft (2,438 mm), which suits a taller room.

Tread

The horizontal surface of a stair step. Related to rise by the comfort formula 2R + T = 24 to 25 in (610 to 635 mm).

Treadmill run-off zone

The clear space behind a treadmill for a fall, set by the machine safety standards at 2 m (6 ft 6 in) long and 1 m (39 in) wide, with 24 in (61 cm) each side. It is the reason a treadmill rarely works against a back wall.

Trickle vent

A background ventilator built into a window head. Approved Document F asks for about 8,000 mm2 (12.4 sq in) of equivalent area in a habitable room, delivered by a slot roughly 400 mm (16 in) long across the frame.

T-turn

The alternative to a turning circle where space is tight: a T-shaped space 60 x 60 in (1,525 x 1,525 mm) overall with arms at least 36 in (915 mm) wide. It suits a corridor junction better than a full circle does.

Turning circle

The clear circle a wheelchair needs to turn through 360 degrees: 60 in (1,525 mm) under the ADA and ICC A117.1, and 1,500 mm (59 in) under Approved Document M. Knee space under a counter may count towards it.

Tweeter height

The reference height for a front speaker, aligned with the seated ear at 38 to 42 in (97 to 107 cm). Surround speakers go higher, about 24 in (61 cm) above ear level, which puts them at 60 to 72 in (152 to 183 cm) from the floor.

Underlay

The layer between subfloor and finish: 2 to 3 mm (1/16 to 1/8 in) of foam under laminate, 5 to 10 mm (3/16 to 3/8 in) of crumb or felt under carpet, and an acoustic mat of about 5 mm (3/16 in) where the flat below needs isolation.

VESA pattern

The bolt spacing on the back of a television, always given in millimetres. 200 x 200 mm (7.9 x 7.9 in) covers screens to about 45 in, 400 x 400 mm (15.7 x 15.7 in) to about 70 in, and 600 x 400 mm above that.

Vestibule

A small enclosed lobby between the front door and the hall, acting as a draught lock. It needs roughly 5 x 5 ft (1.5 x 1.5 m) for both doors to swing, and 48 in (122 cm) clear between the two leaves where the route must be accessible.

Visual weight

How heavy an object looks rather than how heavy it is. Driven by size, colour value, contrast and whether you can see underneath it. The reason a leggy sofa reads lighter than a skirted one of identical dimensions.

Wainscot

Panelling to the lower wall, traditionally at one third of the ceiling height, so 800 to 900 mm (32 to 36 in) under a 2.4 m (8 ft) ceiling. A two-thirds version at 1,500 to 1,600 mm (59 to 63 in) suits a hall or bathroom.

Walk-in closet

A wardrobe you stand inside. One wall of hanging needs 5 ft (1.5 m) of width, two facing walls 7 ft (2.1 m), and an island layout about 12 ft (3.7 m), all built from a 24 in (61 cm) hanging depth plus a 36 in (91 cm) aisle.

Walkway

A route people pass along but do not work in. 36 in (91 cm) is the working minimum, as distinct from a work aisle, which needs 42 to 48 in (107 to 122 cm).

Wall cabinet

An upper kitchen cabinet, 12 to 13 in (30 to 33 cm) deep and 30, 36 or 42 in (76, 91 or 107 cm) high. Its bottom edge normally sits at 54 in (137 cm) from the floor.

Wall-hugger recliner

A chair whose mechanism slides forward as it reclines, needing only 4 to 6 in (10 to 15 cm) behind rather than the 12 to 18 in (30 to 46 cm) a conventional recliner wants. It still projects 65 to 70 in (165 to 178 cm) when open.

Waste factor

The extra material ordered over the measured area: 5 to 10 per cent for a straight tile or plank layout, 15 per cent on the diagonal and 20 per cent for herringbone. A 20 m2 (215 sq ft) floor in herringbone means ordering 24 m2.

Work aisle

A kitchen aisle with worktop on at least one side. 42 in (107 cm) for one cook, 48 in (122 cm) for two, as opposed to a 36 in walkway.

Work triangle

The classic kitchen planning device linking sink, cooktop and fridge, with each leg 4 to 9 ft (1.2 to 2.7 m) and the total 13 to 26 ft (4 to 8 m). Increasingly supplemented by the five-zone model.

Working plane

The height at which illuminance is specified: 30 in (76 cm) for a desk or table, 36 in (91 cm) for a kitchen worktop, floor level for circulation.

Working space

The clear area in front of an electrical panel, 30 in (762 mm) wide, 36 in (914 mm) deep and 6 ft 6 in (1,981 mm) high under the NEC. Nothing may be stored in it, which rules out the panel inside a coat cupboard.

Yoga mat

A mat 24 x 68 in (61 x 173 cm) as standard, 26 x 72 in (66 x 183 cm) for taller users, and 3 to 6 mm (1/8 to 1/4 in) thick. Allow a clear zone of about 7 x 7 ft (2.1 x 2.1 m) for arms extended in any direction.

Missing a term you expected? Tell us and we will add it. For the documents these definitions draw on, see standards, codes and sources.