Spray Foam Insulation Calculator: Board Feet and Kits

Enter the length and height of the area, the openings to leave out, the thickness of foam and the size of your kit. You get the area, the board feet, the board feet with an allowance for waste, and the kits to buy.

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Results

Example job shown. Change the numbers to match yours.

Area to sprayLess the openings: 320 sq ft
Board feet of foamArea × thickness in inches: 960 board feet
Board feet with the extra10% extra for waste: 1,056 board feet

Kits to buy

2 kits

Of 600 board feet

One kit coversAt 3.0 in thick, before waste: 200 sq ft

A board foot of spray foam is one square foot sprayed one inch thick, so the board feet are the area in square feet times the thickness in inches. A kit is sold by its board feet, for example 200 or 600, and covers its board feet divided by the thickness: 600 board feet is 200 square feet at 3 inches. The yield you get depends on the temperature, the surface and how you spray, so the allowance for waste matters, and the maker's instructions set the thickness of each pass. Check the R-value per inch on the data sheet for the foam you buy (open cell and closed cell are different), and wear the protective gear the maker lists.

Before you buy: round up to whole packs, check the size printed on the label, and add a little spare. Your supplier has the final say.

How this calculator works

Worked example: a wall 40 ft long and 8 ft high is 320 sq ft. At 3 in thick that is 960 board feet, and with 10% extra 1,056. With kits of 600 board feet you need 2, and with kits of 200 board feet 6. One 600 board foot kit covers 200 sq ft at 3 in. At 5 in the board feet are 1,600 and the kits 3. Leaving out 40 sq ft of openings gives 840 board feet. An attic roof of 50 × 20 ft at 6 in is 6,000 board feet and 11 kits of 600.

Board feet and kits for common areas, 3 in thick, 10% extra

The board feet, and kits of 200 and 600 board feet.

Area	Board feet	Kits of 200	Kits of 600
100 sq ft	300	2	1
200 sq ft	600	4	2
320 sq ft	960	6	2
500 sq ft	1,500	9	3
800 sq ft	2,400	14	5
1200 sq ft	3,600	20	7

Tips before you buy

Spray in the layers the maker allows: a thick pass in one go can overheat and shrink.
Measure the area, not the room: only the surfaces you spray count.
Use the board feet on the kit label, and compare kits by the cost for each board foot.
Wear a respirator, eye protection and coveralls, and ventilate the space as the instructions say.
Check the code for the thickness and the cover over the foam (some foams need a thermal barrier).

Tools & materials for this project

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Spray foam insulation kit 200 bf Spray foam insulation kit 600 bf Respirator Disposable coveralls Foam trimming knife

Frequently asked questions

How do I calculate board feet of spray foam?

Multiply the area in square feet by the thickness in inches. 320 sq ft at 3 in is 960 board feet.

What is a board foot of spray foam?

One square foot of surface sprayed one inch thick. It is different from a board foot of lumber, which is a volume of 144 cubic inches.

How many kits do I need?

2 kits of 600 board feet for 960 board feet with 10% extra, or 6 kits of 200.

How much area does a kit cover?

A kit covers its board feet divided by the thickness: a 600 board foot kit covers 200 sq ft at 3 in and 200 sq ft at 3 in is 600 board feet.

Should I allow for waste?

Yes, 10 to 15%, because foam is lost on the rough surfaces, the edges and the overspray.

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Related calculators & guides

Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.

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