Calculators
Interior dimension calculators
Calculators that do the arithmetic and then show you the reasoning, because a number without a reason is just a guess with a decimal point.
Short answer
Every calculator here runs entirely in your browser, works in inches or centimetres, and explains the rule it applied. Nothing you enter is stored, sent or logged.
Most interior calculators on the web are a single formula with a form around it, and they hide the formula. These do the opposite: each one applies a documented rule, tells you which rule it used, and flags the cases where the rule stops applying. Where a figure comes from a published standard the page that explains it names the standard.
They are all built the same way: no accounts, no adverts, no data collection, no server round trip. The maths happens in your browser and the page works on a phone in a half-built room with one bar of signal.
- Art hanging height calculatorGives the nail or hook height, not just the centre line, allowing for the wire drop and for the furniture the piece hangs above.
- Bar stool height calculatorSeat height is the counter less 11 in: a 25 in (64 cm) stool under a 36 in (91 cm) counter. Plus knee room, overhang and how many stools a run takes.
- Bathroom layout checkerCheck a bathroom against the IRC and the NKBA guidelines: 15 in (38 cm) to the toilet centre line is the minimum, 18 in (46 cm) is the number to design to.
- Bedroom layout checkerPut a bed, its frame and nightstands into your actual room dimensions and see every clearance that passes, squeaks by or fails.
- Curtain and rod size calculatorWork out rod width and mounting height, finished panel length for the hem you want, and how much fabric width real fullness needs.
- Desk and chair height calculatorSet desk, seat, monitor and footrest heights from your own stature. A 5 ft 9 in adult gets an 18.5 in (47 cm) seat, and the knee space that follows.
- Dining table size calculatorSize a dining table from the number of people, then check whether your room can hold it with chairs pulled out and someone walking behind.
- Gallery wall layout calculatorSix 16 x 20 in frames at a 3 in gap make a 54 x 43 in (137 x 109 cm) block. Get the centre line, the first frame position and the hook height.
- Interior unit converterConvert the numbers that come up while planning a room: 36 in is 91.4 cm and 914 mm, plus square feet, lumens and fabric yards, rounded as the trade rounds.
- Kitchen island fit checkerCheck an island against NKBA aisle widths, see every clearance that fails, and get the largest island your kitchen can actually take.
- Paint quantity calculatorWork out gallons or litres for walls and ceiling, allowing for doors, windows, coats and primer, at realistic coverage rates.
- Pendant and chandelier size calculatorSize a fixture to a table, an island or a room, set its hanging height, and space multiple pendants so they read as one deliberate line.
- Projector throw and screen size calculatorTurn a throw ratio and a lens to screen distance into a screen size. At 156 in (3.96 m) a 1.2 to 1.6 lens gives a 112 to 149 in (284 to 378 cm) diagonal.
- Room lighting lumen calculatorTurn room size, use, ceiling height and surface tone into a lumen target, split across ambient, task and accent layers, with the honest caveats.
- Rug size calculatorEnter your room and the layout you want. Get the standard rug size that fits, the floor border it leaves, and the rule behind the recommendation.
- Shelf span and sag calculatorEnter the span, board and load and get the sag in both units. A 36 in (91 cm) chipboard shelf of hardbacks droops 0.30 in (7.5 mm) on the day it is filled.
- Sofa and seating fit checkerCheck a sofa against your room before you buy. The depth budget, 30 in (76 cm) side walkways, the rug size it forces and whether it turns through the door.
- Stair rise and run calculatorDivide a floor to floor height into legal risers. A 108 in (2.74 m) height gives 15 risers at 7.2 in (183 mm) and a total run of 147 in (3.73 m).
- Tile and flooring quantity calculatorWork out tiles, planks, packs and waste from your room size. A 10 x 12 ft room (3.0 x 3.7 m) takes 60 tiles of 12 x 24 in, and 66 ordered.
- TV size and viewing distance calculatorWork out the right screen size for your seating distance, or the right seating distance for a screen you own, plus the correct mounting height.
- Wallpaper quantity calculatorWork out rolls from drops, not area. An 8 ft (2.4 m) wall with a 21 in (53 cm) repeat yields three drops per roll, and the repeat wastes 9 in on each one.
- Wardrobe and closet plannerSplit a run into long hang, double hang, shelves and drawers. A 96 in (244 cm) run yields 163 in (414 cm) of rail and holds about 154 garments.
How to get the most out of them#
Measure to the face of things, not the wall. Skirting boards, radiators, window boards and door architraves all steal between 1 and 4 in (2.5 and 10 cm), and a plan drawn to the plaster is a plan that fails on delivery day.
Measure three times across a room and use the smallest figure. Almost no domestic room is truly rectangular, and older houses can be out by an inch across a 12 ft span.
Feed the calculators your real furniture, not the catalogue size. Published sofa dimensions frequently exclude the cushion overhang; published fridge depths frequently exclude the handle and the door swing.