Ergonomics for interiors

Pull on almost any dimension in a house and a body comes out of the other end. A 36 in counter is an elbow. A 17 in seat is the underside of a knee. A 36 in walkway is a pair of shoulders with a coat on. A 57 to 60 in art centre is an eye. Once that is visible, interior dimensions stop being a list to memorise and become four or five measurements with rules attached, and the useful skill is knowing which body dimension a given decision is answering and which user it has to answer for.

First decide who, because the average fits nobody#

Anthropometric data is published as percentiles, and the single most consequential choice in this whole subject is which percentile a number serves. It is not a matter of caution. It is determined by the type of dimension.

The 50th percentile serves almost nobody, because no person is average in more than a couple of dimensions at once. Designing an aisle for the median shoulder breadth means half of all adults are squeezed. The percentile sets and their sources are set out in anthropometric data for interior design, and the two populations that break the tables entirely, small children and older adults, are handled in child and older adult dimensions.

The elbow datum: everything you work on#

Comfortable work height is 4 to 6 in (10 to 15 cm) below the elbow for general tasks, less for anything needing force, more for anything needing precision. Standing elbow height across the adult range is 41 to 45 in (104 to 114 cm), which is where 36 in (91 cm) counters come from and also why they suit a person of roughly 5 ft 10 in (178 cm) and nobody shorter.

The corrections are worth stating as numbers rather than principles. A sink is better 2 to 3 in (5 to 8 cm) higher than the general counter because the work happens at the bottom of the bowl. A hob is better 2 to 3 in lower, because the work happens at the top of a pan. Kneading and heavy chopping want 6 to 8 in (15 to 20 cm) below the elbow. Those adjustments, and the dual-height counter that resolves them, are in work surface heights by task and kitchen work heights by user height, with the standard cabinet modules they have to fit inside in kitchen counter and cabinet heights. Seated work is the same rule from a different datum, which is why a desk sits at 28 to 30 in (71 to 76 cm) and a sit-stand desk has to cover a 22 in (56 cm) range: see standing desk heights and sit-stand ranges.

The knee datum: everything you sit on#

Seat height is capped by popliteal height, the distance from the underside of the knee to the floor when seated, which runs 15.5 to 19 in (39 to 48 cm) across the adult range. A seat higher than the shortest user's popliteal height puts their weight on the underside of the thigh, and 17 in (43 cm) recurs everywhere for that reason.

Depth is capped the same way, by buttock to popliteal length, roughly 17 to 21 in (43 to 53 cm). A sofa 24 in (61 cm) deep supports the back of anyone tall enough and nobody else, which is why deep sofas come with cushions and footstools that are really depth corrections. Angle then trades against both: every degree of recline lets the seat sit lower and deeper. The whole set is in seat height, depth and angle, and the version for a chair that adjusts under you in office chair dimensions and adjustment ranges.

The eye datum: everything you look at#

Standing eye height runs 59 to 68 in (150 to 173 cm) and seated eye height 44 to 49 in (112 to 124 cm) above the floor. Two rules come out of it. Art is centred at 57 to 60 in (145 to 152 cm) because that suits standing eye height across the range, as art hanging height sets out. Screens are centred nearer 42 to 48 in (107 to 122 cm) because you watch them sitting down, and the tolerance for looking up at a screen is far smaller than for looking down at one.

The seated figure is also what makes a mirror, a shelf or a kitchen pass-through work or fail, and the geometry of all of them is in eye level and sightlines, seated and standing. Viewing distance is the other half of the same calculation, worked through in screen size and viewing distance.

Reach, and the storage that follows from it#

The comfortable band runs 30 to 60 in (76 to 152 cm) above the floor, the stretch band to about 72 in (183 cm), and everything above that needs a step. Accessible design tightens the same idea to a 15 to 48 in (38 to 122 cm) range, and the two converge on the same practical advice: put daily items in the middle band, weekly items above and below it, and annual items at the extremes. The bands, the depth penalty and the storage frequency logic are in reach zones and useful storage heights, with the code figures in accessible reach ranges and the shelf dimensions that sit inside them in shelf depth and vertical spacing.

Breadth, and the clearances that follow from it#

The last datum is the plan one. Shoulder breadth is 18 to 20 in (46 to 51 cm), body depth 9 to 13 in (23 to 33 cm), and a person moving rather than standing needs about 24 in (61 cm). Two people passing without either turning need 42 to 48 in (107 to 122 cm), which is exactly where comfortable hallway and walkway widths land in walkway and circulation widths at home. Anything carried adds 6 to 12 in (15 to 30 cm) to effective width, and working back to back at two counters needs more again. The full set is in clearance for two people to pass and work.