Foam Thickness Guide by Furniture Type: Sofas, Chairs, Stools & More

Order foam too thin and the seat bottoms out; too thick and the piece looks bloated and the cover won’t fit. This guide gives working thicknesses by furniture type, straight from the cutting list we use in the workshop, along with the density to pair with each.

Two numbers, not one

Thickness alone doesn’t describe a cushion. A 50 mm slab of soft 22 kg/m³ foam will bottom out on a bar stool; 50 mm of firm HR35 will not. So every line below gives a thickness and a density. If you only have budget for one upgrade, spend it on density – see Foam density and firmness explained.

Standard sheets from our foam & padding range are 2000 × 1000 mm in 25, 50, 75 and 100 mm. Thicker cushions are made by laminating layers, which also lets you put a softer top over a firmer base.

Foam thickness guide by furniture type

Furniture	Seat thickness	Density	Notes
Dining chair (drop-in seat)	25–50 mm	HR35 or 32 kg/m³ firm	Over ply base; 50 mm for long dinners
Dining chair (sprung seat)	25 mm	30–35 kg/m³	Springs give the depth
Bar stool / kitchen stool	50 mm	HR35 firm	Small area, high load – don’t go soft
Bench / window seat	50–75 mm	HR35	75 mm for reading; 50 mm for perching
Sofa seat cushion (loose)	100–120 mm	HR35	Laminate 100 + 25 mm for 125 mm
Sofa seat (fixed, on springs)	50–75 mm	HR35	Plus Dacron; springs supply the bounce
Sofa back cushion	75–100 mm	22–28 kg/m³ soft	Or foam core + fibre envelope
Armchair seat	100 mm	HR35	Same as sofa
Armchair arm pads	25 mm	28–32 kg/m³	Over wadding
Ottoman / footstool	50–75 mm	HR35	Doubles as seat – firm
Headboard	25 mm	25–30 kg/m³	50 mm for deep buttoning
Day bed / sofa bed mattress	100 mm	HR35 or better	120 mm for nightly use
Boat squab	50–75 mm	Dry-fast or HR35	See our boat squab foam guide
Campervan bed	100 mm	HR35	Weight vs comfort compromise
Office / desk chair	50–75 mm	HR35 firm or higher	All-day load
Church pew / hall bench	50 mm	HR35 firm	Fire-rated grade for public venues

Why these numbers work

Seats: 100 mm is the lounge standard

For a loose sofa cushion the body compresses HR35 by roughly 30–40% under normal sitting. At 100 mm that leaves 60 mm of foam between you and the deck, which is enough that you don’t feel the springs or webbing. At 75 mm a heavier adult will feel the base on a firm deck; at 125 mm and above the seat height creeps up and the sofa starts to look overstuffed unless the frame was designed for it.

Dining and stools: firm and thin beats soft and thick

A dining seat is only 400–450 mm square and the whole body weight lands on it. Thick soft foam here makes the sitter feel like they are perching on a balloon. 50 mm of firm HR35 over a solid base is the trade standard for a chair that will be sat on for two-hour dinners. For drop-in seats where the chair rail height is fixed, 25 mm firm plus wadding keeps the seat from sitting too proud.

Backs: soft and thick

Backs carry little load, so density can drop and thickness can rise. The point is enveloping softness. Many workshops don’t use foam at all in loose back cushions; a foam core in a fibre envelope gives the best of both.

Adjusting for the sitter and the frame

• Heavier users (100 kg+): keep thickness, move up a firmness grade in HR35 rather than adding 25 mm – thicker soft foam just sinks further.
• Elderly or mobility issues: firmer and slightly thinner so the seat height stays high and it is easier to stand from.
• Low frames: a 125 mm cushion on a low mid-century frame changes the whole proportion. Match the original thickness.
• Fixed seats over sinuous springs: springs provide 20–30 mm of give, so 75 mm foam feels like 100 mm of loose cushion.
• Solid ply bases: no give underneath, so use the upper end of the range.

Layering to fine-tune feel

The best sofa cushions are rarely one block. A typical trade lamination for a 125 mm cushion is 100 mm HR35 with 25 mm of softer 28 kg/m³ foam on top, then a 200 gsm Dacron wrap. You get firm support and a soft first touch. Bond layers with upholstery spray adhesive, mist both faces, wait 30 seconds, then press together – or order the cushion cut and laminated through our contact page.

Thickness for cushions you lie on

Sofa beds, day beds and van beds are a different calculation because a lying body spreads its weight over a large area. Pressure points are the hips and shoulders, and the foam only needs to be thick enough that those don’t reach the base. At HR35, 100 mm is comfortable for occasional guests and 120–150 mm for nightly use. A 25 mm soft or memory-foam top layer improves the sleep surface without adding bulk when the piece is used as a seat during the day.

Allow for the wrap and the cover

Dacron adds roughly 5–10 mm to a cushion before it settles, so a cover with a 120 mm boxing takes 120 mm foam plus wrap, not 130 mm foam. If you want a tight, tailored look with no wrap, go 10 mm thicker than the boxing. Full measuring instructions are in How to measure and order replacement sofa cushion foam.

Commercial and public seating

Cafés, offices and venues usually need a fire-rated foam to meet AS/NZS 1530.3 or the group number requirements of a fit-out. Thickness rules are the same, but specify the grade at ordering time and keep the certificate. If the job is a fit-out in Auckland, our sister workshop Upholstery World does commercial upholstery on-site with compliant materials.