Cushion Foam Calculator
Turn cushion dimensions and a count into the total foam volume in cubic metres and board-feet, and the finished mass at the density you pick.
Foam needed
Each cushion is treated as a rectangular block. Real cushions box, taper, and compress under their covers, so order a little extra thickness for shaping.
Volume, density, and how a cushion lasts
When you refill sagging sofa cushions, two numbers do most of the work: how much foam the job takes, and how dense that foam is. Volume is simple geometry — length by width by thickness, times the number of cushions — and it tells you how much to order, whether you buy by the cubic metre or the board-foot.
Density is what separates a cushion that holds up from one that flattens in a season. Because density is a mass per unit volume, multiplying it by the volume gives the finished mass, a handy cross-check against a foam’s spec and a fair way to compare grades. Seat cushions generally want a firmer, denser foam than backs; this tool reports both figures so you can weigh cost against longevity.
Frequently Asked Questions
How is cushion foam volume calculated?
Each cushion is treated as a rectangular block: length × width × thickness. Entered in centimetres, that gives a volume in cubic metres, which the tool multiplies by the number of cushions and also converts to board-feet — the unit upholstery foam is often sold and priced in (one board-foot is a 12 × 12 × 1 inch piece).
What foam density should I use for a sofa cushion?
Sofa seat foams commonly fall around 30–50 kg/m³. Density is the single best guide to how a foam behaves: higher-density foam supports more weight before bottoming out and keeps its shape far longer, which is why it costs more. Seat cushions usually want a firmer, denser foam than back cushions. Density is separate from firmness — a dense foam can still feel soft — so check the specific foam's spec.
Why does the tool also show mass?
Multiplying volume by density gives the finished mass of the foam. It's a quick way to sanity-check a foam grade against its data sheet and to compare options: if a same-size cushion comes out much lighter, the foam is lower-density and will likely soften sooner.
Should I order a bit extra?
Yes. A finished cushion is boxed, tapered, and compressed inside its cover, and foam is trimmed and glued during shaping, so a plain rectangle is a minimum. Order a little extra thickness for sculpting and wrap the foam in a layer of batting for a fuller, longer-lasting look.
Does this work for both seat and back cushions?
It works for any cushion you can measure as a block — seat, back, or bolster — one shape at a time. Run it once per size of cushion, entering the count for that size, and add the totals together for the whole sofa.
Estimates for planning — not professional interior-design advice. Check the specific foam’s data sheet for its density and load rating, and measure your cushions before ordering.