Chair Seat Depth and Lumbar Support: How to Check Fit Without a Showroom
Chair fit is mostly about two numbers — your seat depth and your lumbar curve height — and both can be measured at home with a tape measure and a wall.
Measuring your seat depth
Seat depth is the distance from the back of the seat to the front edge. The correct fit leaves a gap of 5-8cm between the back of your knee and the front edge of the seat when you're sitting fully back against the chair. Too deep, and the front edge presses into the back of your knees, restricting circulation. Too shallow, and your thighs lack support.
To measure what you need: sit on any flat surface against a wall, measure from the wall to the back of your knee, then subtract 6cm. That's your target seat depth.
Finding your lumbar curve height
Your lumbar curve — the inward curve of your lower back — sits roughly 15-23cm above the seat surface for most adults, though this varies with torso length. To find your own number: sit upright against a wall, slide a hand behind your lower back to find the deepest point of the curve, and measure from the seat to that point.
| Torso length (seated, hip to shoulder) | Approx. lumbar support height |
|---|---|
| Shorter torso (under 55cm) | 15-18cm |
| Average torso (55-65cm) | 18-21cm |
| Longer torso (over 65cm) | 21-24cm |
Checking fit from an online listing before buying
Most chair listings give an overall seat depth range (often adjustable from 42-48cm) and sometimes a lumbar height adjustment range. Compare both directly against the two numbers you just measured. If a listing only gives one fixed seat depth with no adjustment range, treat that number as the depth you'll be stuck with — there's no "it'll loosen up" with seat foam.
Adjustable vs. fixed lumbar support
A height-adjustable lumbar pad (one that slides up and down independent of seat height) is worth prioritizing over a fixed lumbar curve built into the backrest shape, because the fixed version only fits people within a narrow torso-length range — and you won't know if you're in that range without a showroom test.
Red flags in product descriptions
- "Ergonomic design" with no specific adjustment ranges listed
- Seat depth not listed at all (common in budget listings — ask via the listing's Q&A if unclear)
- Lumbar support described only as "built-in curve" with no height adjustment
- No weight rating listed, which often correlates with thinner gas cylinder/base components