CUSHIONFUN

🧱 Cushion Foam Calculator

Enter your cushion size, quantity, and use to get the total foam volume in board feet and cubic feet — plus a recommended foam firmness (ILD) and density for seats, backs, and outdoor cushions.

🧮 Size Your Foam

Foam is sold by the sheet or cut-to-size. One board foot is a 12×12×1″ slab (144 in³). Add a thin polyester wrap over seat foam for a rounded, upholstered edge.

Polyurethane foam burns readily. Keep it away from heaters, open flames and other heat sources, and check the flammability label on the foam you buy: the rules for indoor furniture foam differ from region to region and from outdoor foam. This calculator sizes foam; it makes no fire-safety claim.

🧱 Foam needed

Total foam volume
32 board ft (2.67 ft³)
Volume per cushion2304 in³
Total volume4608 in³
Board feet32
Cubic feet2.67 ft³
Recommended firmness~35 ILD (medium-firm)
Recommended density1.8 lb/ft³ high-density

Seat cushions carry your weight, so choose a high-density foam (~1.8 lb/ft³) at roughly 35 ILD — medium-firm, so it feels supportive without going soft or bottoming out over time.

Get the foam and the firmness right

Foam is priced by volume and cut to order, so knowing your board feet up front saves money and awkward returns. Just as important is choosing the right firmness — the wrong ILD is why a new seat cushion feels either rock-hard or sags within weeks.

This calculator gives the volume in the units suppliers use and pairs it with clear ILD and density guidance for seats, backs, and weather-exposed outdoor cushions, so you order foam that fits and lasts.

❓ Frequently Asked Questions

How is the foam volume measured?

It multiplies length × width × thickness for one cushion, then multiplies by the quantity. A board foot — how foam is often priced — is a slab 12 × 12 × 1 inch, or 144 cubic inches, so the tool divides the total by 144 for board feet and by 1728 for cubic feet.

What firmness (ILD) should I choose for a seat?

ILD, or Indentation Load Deflection, measures firmness — higher is firmer. For seat and bench cushions that carry weight, use a high-density foam (around 1.8 lb/ft³) at roughly 35 ILD, a medium-firm feel that supports you without bottoming out or going soft within a season.

What about back cushions and outdoor cushions?

Back cushions only need to feel plush, so a softer foam around 18–24 ILD — or a foam core wrapped in polyester batting — is ideal. Outdoor cushions should use reticulated dry-fast foam: its open-cell structure lets rain drain straight through and air-dry, which resists mildew. Aim for a medium-firm 30–35 ILD outdoors.

Should I wrap the foam?

For seat cushions, a thin layer of polyester batting or Dacron over the foam rounds the edges, prevents that boxy look, and helps the cover glide on. It also adds a touch of softness over a firm core — the best of both: supportive to sit on, soft to the touch.

Is cushion foam a fire risk?

Yes, polyurethane foam is flammable and burns quickly once lit. Keep foam cushions away from heaters, fireplaces and open flames, and read the flammability label on any foam you buy: furniture-foam rules differ by region, and outdoor foam is often labeled differently from indoor foam. This calculator only sizes the foam; it does not tell you whether a foam meets any fire standard.