Fit and posture guides

Every number on this site comes from one module, computed from a cited anthropometric table. These are the pages that show the arithmetic.

Maintained by Sawyer V. · Last updated September 30, 2026

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A tape measure beside an office chair at a desk

Most seating advice is adjectives. "A good height for most people." "Comfortable support." "Suitable for tall users." None of that lets you check anything, which is exactly why it gets written that way.

These pages are arithmetic instead. Every fit figure on this site - in these guides, in every roundup's per-pick fit column, in every comparison table - is computed by one module from one cited source: the British adult percentile table published in Pheasant and Haslegrave's *Bodyspace*. Because it is one module, the site cannot contradict itself, and because the source is named you can go and check it.

Start with these three

[Seat height and seat depth by your height](/guides/seat-height-by-your-height) is the foundation. Two measurements decide whether a chair fits you, and neither is your height: your popliteal height (floor to the underside of your thigh, seated) and your buttock-popliteal length (which sets your maximum seat depth). The table converts from standing height; measuring your own beats it.

[What stool height does a standing desk need?](/guides/stool-height-for-a-standing-desk) is the one that saves money. Your desk height minus your sitting elbow-rest height, published as 7.5 to 11.4 inches. A 42-inch desk needs a seat around 31 to 34 inches - and published ceilings across the stools on this site run from 24 inches upward, all of them sold as standing-desk stools.

[Office chair weight capacity](/guides/office-chair-weight-capacity) explains why a 500 lb claim and a 500 lb chair are different things. The answer is which BIFMA standard was used: X5.1 tests around a 275 lb occupant, X5.11 covers 253 to 400 lb with most loads raised - and X5.11 is the only standard that specifies a minimum seat width.

What the guides are for

Fit tables - three pages of computed numbers, which is where every other page on the site gets its figures.
How-to guides - setting up a kneeling chair or a saddle stool, both of which fail more often from setup than from geometry.
Evidence guides - whether anti-fatigue mats and lumbar support do what is claimed, with the boundary between mechanism and outcome stated rather than blurred.
Definitions - what a perch stool, a drafting chair and a wobble stool actually are, since all three are sold under names that overlap.

The two measurements worth taking

If you do one thing from this whole section, do this. It takes a minute and it makes every product page on the internet more useful to you.

Popliteal height. Sit on a hard, flat surface, feet flat, knees at a right angle, in the shoes you work in. Measure floor to the underside of your thigh right behind the knee. That figure is your seat height, as measured - no allowance needed, because the shoes are on.
Buttock-popliteal length. Same position. Measure from the back of your buttock to the back of your knee. Subtract 2 inches, and that is your maximum seat depth.
Then check any chair against both. Your seat height should fall inside its published range with an inch of margin at each end; its published depth should be at or under your maximum. A chair failing either is the wrong chair however good it is.

Where the guides stop

Deliberately, at the edge of what published figures can tell you. These pages describe mechanism - where load goes, what the published angles are, what adjusts. They do not make clinical claims, because there is no clinician on this site and nothing here is medically reviewed.

That boundary is most visible on the back-pain and sciatica material, where it would be easy and lucrative to blur it. We describe what a seat mechanically does and then stop. If you have persistent or worsening pain, numbness, tingling or weakness, a clinician is the right next step and no product on this site is a treatment.