Spray Foam Insulation Calculator: Board Feet, Kits & Cost
Board feet of spray foam for your wall, roof or floor from its area and a thickness or the R-value you need, with sets, kits and cost.
By Marko VisicBSc Physics, University of Ljubljana
960board feet
3 in of closed-cell foam, R-22.2
1 set of Huntsman Heatlok HFO High Lift
- Area
- 320 sq ft
- Thickness
- 3 in
- R-value
- R-22.2
- To buy
- 960 bd ft
- Sets
- 1
- Passes
- 1
Huntsman Heatlok HFO High Lift is rated R-7.4 per inch and yields 4,500 board feet a set, the low end of its range. It goes on up to 6.5 in a pass. Yields are theoretical: worked out in laboratory conditions, so add some extra for loss on the job.
960 board feet, 3 in of closed-cell foam at R-22.2, 1 set
Spray foam is sold by the board foot, a square foot of foam an inch thick. A 40 by 8 ft wall with 3 inches of closed-cell foam takes 960 board feet, R-22.2 at Heatlok HFO High Lift’s 7.4 per inch: 1 set at its low-end yield, or 5 Froth-Pak 200 kits.
Open-cell foam needs twice the thickness of the closed-cell foam here for the same R-value, so the R-value you need sets the board feet as much as the area does.
How to calculate spray foam insulation
Measure the area to be sprayed, pick the thickness, and multiply. One board foot is one square foot of foam one inch thick, which is how sets and kits are rated. To size by R-value instead, divide the R-value by the foam’s R per inch to get the thickness.
Board feet = area (sq ft) × thickness (in)
Thickness = target R-value ÷ R per inch
Sets or kits = board feet ÷ yield per set or kit, rounded up
Example: a 40 by 8 ft wall is 320 sq ft. Three inches of closed-cell foam is 960 board feet, and at 7.4 per inch it reaches R-22.2. One set of Heatlok HFO High Lift covers it at the low end of its yield; in Froth-Pak 200 kits it takes 5, at 2 inches a pass, so two passes.
How much spray foam insulation do I need
The R-value you need sets the thickness, and the thickness times the area sets the board feet. The table works it out per 100 sq ft for each foam the calculator offers. Take the R-value from your energy code, or from ENERGY STAR’s levels by climate zone in the insulation thickness chart.
| Target | Open-cell (R-3.7/in) | Closed-cell (R-7.4/in) | Closed-cell kit (R-6.2/in) |
|---|---|---|---|
| R-13 | 3.5 in, 351 bd ft | 1.8 in, 176 bd ft | 2.1 in, 210 bd ft |
| R-15 | 4.1 in, 405 bd ft | 2 in, 203 bd ft | 2.4 in, 242 bd ft |
| R-21 | 5.7 in, 568 bd ft | 2.8 in, 284 bd ft | 3.4 in, 339 bd ft |
| R-30 | 8.1 in, 811 bd ft | 4.1 in, 405 bd ft | 4.8 in, 484 bd ft |
| R-38 | 10.3 in, 1,027 bd ft | 5.1 in, 514 bd ft | 6.1 in, 613 bd ft |
| R-49 | 13.2 in, 1,324 bd ft | 6.6 in, 662 bd ft | 7.9 in, 790 bd ft |
At these ratings closed-cell foam reaches a given R-value in half the depth of open-cell foam, which matters where the framing is shallow.
Spray foam R-value chart
Each product has its own rating. Huntsman rates Heatlok HFO High Lift at R-7.4 per inch and Classic Ultra Select open-cell foam at R-3.7 at an inch; DuPont rates Froth-Pak at R-6.2 at an inch and R-12.2 at two. The chart multiplies each rating by the thickness.
| Thickness | Open-cell (Huntsman Classic Ultra Select) | Closed-cell (Huntsman Heatlok HFO High Lift) | Closed-cell kit (DuPont Froth-Pak 200) |
|---|---|---|---|
| 1 in | R-3.7 | R-7.4 | R-6.2 |
| 2 in | R-7.4 | R-14.8 | R-12.4 |
| 3 in | R-11.1 | R-22.2 | R-18.6 |
| 4 in | R-14.8 | R-29.6 | R-24.8 |
| 5 in | R-18.5 | R-37 | R-31 |
| 6 in | R-22.2 | R-44.4 | R-37.2 |
The Department of Energy’s 2010 home insulation guide gives an older, independent check: open-cell foam at R-12.6 for 3.5 inches and closed-cell foam at R-6.5 for an inch.
Spray foam kits and sets
Contractors spray from sets, two drums mixed at the gun; homeowners and small jobs use two-cylinder kits. Both are rated in board feet of theoretical yield, which Dow’s fact sheet describes as worked out in perfect laboratory conditions, without the blowing agent lost or the way the foam is sprayed. Plan on getting less, and add extra in the calculator.
| Product | Type | Yield | Thickest pass |
|---|---|---|---|
| Huntsman Classic Ultra Select | Open-cell set | 19,500 bd ft (annual average) | not given |
| Huntsman Heatlok HFO High Lift | Closed-cell set | 4,500 to 5,000 bd ft | 6.5 in |
| DuPont Froth-Pak 200 | Closed-cell kit | about 200 bd ft | 2 in |
For the 320 sq ft example wall at R-21, open-cell foam takes 1,816 board feet, a fraction of one set; closed-cell takes 908 board feet, also under one set, or 6 Froth-Pak 200 kits.
Spray foam insulation cost
Spray foam is priced by the board foot. A price per square foot only makes sense with a thickness: at three inches, a square foot is three board feet, so its price is three times the price per board foot. Kits are priced by the kit, so divide the kit price by its yield to compare them with a contractor’s quote.
Enter your price per board foot in the calculator to see the cost. We don’t list typical prices: we found no current public source for them, and the Department of Energy’s 2010 insulation guide, the last federal table we know of, is too old to price a job today.
Covering spray foam
Foam inside a house is normally covered. Huntsman’s data sheet says Classic Ultra Select must be covered with ½ in gypsum board or one of the intumescent coatings it lists, and DuPont rates Froth-Pak Class A up to 2 inches thick. In a crawl space, the crawl space encapsulation guide covers where wall insulation goes under the 2021 IRC.
Spray foam calculator FAQ
How many board feet of spray foam do I need?
Multiply the area in square feet by the thickness in inches. A 40 by 8 ft wall is 320 sq ft; at 3 inches that is 960 board feet.
How thick should spray foam be?
As thick as the R-value you need divided by the foam’s R per inch. For R-21 that is 5.7 inches of an open-cell foam rated R-3.7 per inch, or 2.8 inches of a closed-cell foam rated R-7.4.
How much area does a spray foam kit cover?
DuPont’s Froth-Pak 200 yields about 200 square feet at an inch thick, so 66.7 sq ft at 3 inches. That is a theoretical yield, worked out in laboratory conditions, so real jobs get less.
What is the R-value of spray foam per inch?
It depends on the product. Huntsman rates Heatlok HFO High Lift closed-cell foam at R-7.4 per inch and Classic Ultra Select open-cell at R-3.7; DuPont rates Froth-Pak at R-6.2 at an inch. The Department of Energy’s 2010 guide listed closed-cell foam at R-6.5 for an inch.
How much does spray foam insulation cost?
Installers price it by the board foot, or by the square foot at a set thickness, and kits sell by the kit. Multiply the board feet by your price per board foot; the calculator does it when you enter a price. We don’t list typical prices because we found no current public source for them.
Does spray foam have to be covered?
Inside a house, usually. Huntsman’s data sheet says Classic Ultra Select must be covered with ½ in gypsum board or a listed intumescent coating, and DuPont rates Froth-Pak Class A up to 2 inches thick. Your building department has the final word.
Sources & method
Board feet are the area in square feet times the thickness in inches; sized by R-value, the thickness is the R-value divided by the product’s R per inch. Sets and kits are the board feet, plus any extra you add, divided by the maker’s yield and rounded up, using the low end of Huntsman’s range for Heatlok HFO High Lift. Ratings and yields are from Huntsman’s and DuPont’s product data, the yield definition from Dow’s Froth-Pak fact sheet, and the independent check from the Department of Energy’s 2010 guide.
- Huntsman Building Solutions. Heatlok HFO High Lift Sell Sheet (AN 20.00060). REV 06.21.22
- Huntsman Building Solutions. Classic Ultra Select Technical Data Sheet (AN 20.00178). REV 02.10.22
- DuPont. Froth-Pak 200 Insulation & Sealant Spray Foam System Kit. retrieved Nov 15, 2026
- U.S. Department of Energy. Guide to Home Insulation (DOE/EE-0340). October 2010
- Dow Building Solutions. FROTH-PAK Two Component Quick-Cure Polyurethane Foam Insulation, Manufacturer's Insulation Fact Sheet (Form 179-06108-1213). Form 179-06108-1213
- Roof Square Footage Calculator: Area & Roofing SquaresThe roof surface, for foam sprayed under the roof deck.
- Insulation Thickness Chart: R-38 to R-60 by MaterialHow many inches each R-value takes in batts, blown-in insulation and foam.
- Crawl Space Encapsulation: What the Code RequiresCrawl space wall insulation by climate zone under the 2021 IRC.