Bar stool seat height after upholstery: pad thickness, foam compression and the clearance the counter actually gets

A bar stool ordered at 750 mm arrives at 782 mm, sits at 770 mm when someone is on it and clears the counter by 218 mm instead of 250 mm. Every one of those numbers is predictable before the frame is cut, and every one of them is argued about after the first container lands. This is the arithmetic we use on bar runs.

Published by JPChairs · Chair manufacturer in Foshan, China · 2026-11-04

Why the drawing height is not the height you get

A frame welded to 750 mm is a frame, not a seat. Add a 35 mm foam pad and 1.2 mm of vinyl and the finished seat top lands at 782 to 785 mm. The pad is cut 2 to 4 mm oversize and pulled over the pan, so the crown sits about 5 mm above the front edge, and the crown is not the measuring point.

Measure at the front edge, unloaded, 24 hours after upholstery. Measured that way, 20 stools out of one run spread across 6 to 9 mm, because foam blocks come back from the cutter within 1 mm but the pull-over tension varies by operator. A plus or minus 5 mm tolerance therefore needs the run sorted into height bands; plus or minus 10 mm ships as it comes off the line. Decide which one you are buying before the PO, not after.

What 80 kg does to a 35 mm pad

A 35 kg per cubic metre foam at 35 mm thickness reads a 25 per cent indentation force of roughly 110 to 140 N on a 200 mm disc, measured to ISO 2439. An 80 kg guest puts about 785 N through a 400 x 400 mm seat, or 4.9 kPa, and compresses the pad 30 to 38 per cent, which is 11 to 13 mm.

• 80 kg guest: seat height drops from 782 to about 770 mm.
• 50 kg guest: 8 mm of compression, 774 mm.
• 110 kg guest: 17 mm, 765 mm.
• Cheap 25 kg per cubic metre foam: 18 to 22 mm, and 4 mm of that is permanent after one season.

Permanent set is the number that matters over a three-year fit-out. Test D of ASTM D3574 holds the sample 22 hours at 70 C and allows 5 per cent loss, which is 1.7 mm on a 35 mm pad. Foam that loses 12 per cent leaves every stool in the room 4 mm lower than the one next to it, and guests feel that as a wobbly row rather than as foam.

Counter clearance: the arithmetic from 1,050 mm down

Take a 1,050 mm bar top, 30 mm of top thickness and a 20 mm subframe, and the underside sits at 1,000 mm. The 250 mm clearance rule puts the seat at 750 mm, which is where the drawing started.

Upholster it and the clearance becomes 218 mm. A 95th percentile thigh is 190 to 200 mm at the front edge, so 218 mm still passes with 18 mm to spare, but the margin that made the layout comfortable is gone. Below 210 mm guests turn sideways to get in and the stool reads as too tall for the counter, even though the frame is the height that was specified.

Two ways out, both cheaper than re-cutting frames: lower the frame to 720 to 730 mm when a 35 mm pad is specified, or keep 750 mm and use a 20 mm pad. What does not work is ordering 750 mm frames, adding pads on site and then blaming the counter.

The footrest has to move with the pad

A footring sits 200 to 300 mm below the seat front edge, which on a 750 mm stool means 450 to 550 mm above the floor. Add 32 mm of upholstery and leave the ring where it is, and the ring-to-seat distance drops to 250 to 282 mm from 280 to 312. That changes knee angle from about 100 to 105 degrees to 92 to 96, pushes the guest's hips back on the seat and puts load on the front third of the pad.

The rule we build to: set the top of the footring 260 to 280 mm below the finished seat top. At 782 mm that is 502 to 522 mm above the floor, so a 510 mm setting with plus or minus 10 mm covers the whole run. On a swivel stool check the ring under load as well, since the column settles 3 to 5 mm under an 80 kg guest.

Three measurements per stool, five stools per hundred

• Unloaded height: front edge, 24 hours after upholstery, at 20 C and 55 per cent relative humidity.
• Loaded height: 80 kg plate, 60 second hold, read at 5 seconds, then again after 5 minutes of recovery. Recovery within 2 mm means the foam is still doing its job.
• Pad firmness: 25 per cent indentation force within 15 per cent of the approved sample, measured on the same disc diameter.
• Run spread: sample 5 per 100. If the spread exceeds 8 mm, sort into bands instead of shipping a mixed container.

We cut pads on the factory foam cutting tables and log all three readings against the carton number, so a site can tell which pallet a short stool came from without opening it.

What to put in the PO so the height is enforceable

• State the finished seat height, not the frame height. Example: 782 mm finished, plus or minus 5 mm, front edge, unloaded.
• Specify the pad: 35 mm, 35 kg per cubic metre, 25 per cent indentation force 110 to 140 N, vinyl 1.2 mm, compression set 5 per cent or less.
• Set the footrest by finished height: top of ring 510 mm plus or minus 10 mm above the floor.
• Require the numbers on the packing list, five stools per lot.

Written that way, a 30 mm discrepancy is a claim rather than a discussion. On the seating side the same discipline applies to our commercial bar stools at fixed seat heights, where the height is quoted finished rather than welded for exactly this reason.