Spray Foam Insulation Calculator — Board Feet & Kits
Enter the area you want to insulate and the foam thickness. This calculator gives you the board feet of coverage needed and how many DIY spray foam kits to buy.
How to use this calculator
- Enter the total area you are insulating in square feet.
- Enter the foam thickness — 2 inches of closed-cell or about 3.5 inches of open-cell for walls.
- Choose your kit size. The calculator adds ~10% because rated yields are optimistic in real use.
- For sealing gaps rather than covering area, a single-can foam is cheaper than a kit.
The formula
Spray foam is sold by the board foot — the volume that covers 1 square foot at 1 inch thick.
Board feet = area (sq ft) × thickness (in). So 200 sq ft at 2 inches = 400 board feet.
Kits = board feet ÷ kit yield, rounded up. Rated yields assume ideal conditions, so add about 10% for waste, temperature, and technique.
Worked example
200 sq ft of wall at 2 inches of closed-cell foam, using 600 bd ft kits.
Board feet = 200 × 2 = 400 board feetWith 10% loss = 440 board feetKits = 440 ÷ 600 = 0.73 → 1 kit
You need 1 × 600 board foot kit for 200 sq ft at 2 inches thick.
Frequently asked questions
What is a board foot of spray foam?
A board foot is one square foot of coverage at one inch of thickness. A "600 board foot" kit covers 600 sq ft at 1 inch, 300 sq ft at 2 inches, and so on.
How many board feet do I need?
Multiply the area by the thickness in inches. 500 sq ft at 2 inches needs 1,000 board feet. Add about 10% because real yields fall short of the rating.
How thick should spray foam be?
For closed-cell foam, about 2 inches in walls and 3 inches at rim joists meets common code R-values. Open-cell needs roughly twice the thickness for the same R-value.