What is a board foot of spray foam?

One square foot sprayed one inch thick, which is 144 cubic inches (12 × 12 × 1 in), the same board foot lumber is sold by. So board feet = square feet × inches: 100 sq ft at 3 in is 300 board feet, and the same 300 board feet covers 150 sq ft at 2 in.

How many spray foam kits do I need?

Work out the board feet, add waste, and divide by the board feet on one kit. A 40 × 8 ft wall (320 sq ft) at 2 in is 640 board feet, 736 with 15% extra, which is 1.13 of a 650 board foot kit, so 2 kits. Without the extra it is 0.98 of a kit, so 1 kits. Kits come whole, so a small shortfall means another kit.

Why does a kit cover less than its label says?

Kit makers state the board feet for a 1 in layer under ideal conditions (Revchem’s Froth-Pak information sheet says theoretical yields are lab figures and that actual coverage will be lower). Cold chemical or surfaces, an uneven spray, overspray and trimming all use foam. That is what the waste setting is for: 10%, 15% and 25% are this calculator’s own estimates, so adjust them to your skill and conditions, or buy a spare kit.

Open-cell or closed-cell foam?

Per inch, closed-cell foam insulates about 6 against 3.6 for open-cell (U.S. DOE Building America figures), so it reaches a given R-value in about 60% of the thickness. For R-13, closed-cell takes 2.25 in and open-cell 3.75 in. Closed-cell is the denser foam and open-cell the lighter. Most DIY two-component kits, including Froth-Pak and Touch ’n Seal, are closed-cell, with open-cell kits also sold. Other sources quote slightly different ranges (about 3.5 to 3.8 open-cell, about 6 to 7 closed-cell), so use your product’s data sheet when you have it.

How thick should spray foam be?

Thick enough for your target R-value, within what the building and the product allow. Divide the target by R per inch: closed-cell R-13 is 2.25 in and R-19 is 3.25 in at 6 per inch. The R-value to aim for depends on your climate zone and the part of the house; ENERGY STAR hosts the U.S. Department of Energy table (linked in the sources), and this page does not copy its numbers. Kits are sprayed in thin passes, so a thick layer is built up in several lifts; follow the kit’s data sheet for the maximum per pass.

Do I subtract the studs or joists?

Foam is sprayed on the whole surface and covers the framing it touches, so the area is the wall or roof as measured. Subtract only doors, windows and other openings you will not spray. If you only fill the cavities between studs, the board feet are the cavity area × the depth; the extra on the framing faces is what the waste setting covers.

Can I use this for a roof deck or an unvented attic?

Yes for the quantity: enter the length and width of the underside of the roof deck (the sloped area, not the attic floor), pick the thickness or the R-value, and read the board feet and kits. Whether the design is allowed, and the thickness it needs, is a code and building-science matter, as is the attic ventilation: see the attic ventilation calculator and ask your local building department before you spray.

How does this compare with batts or blown-in?

Foam is counted in board feet and kits; batts and blown-in are counted in bags by the square feet or the bags per 1,000 sq ft on the package. Use the insulation calculator for the bag counts, and compare on R-value and cost for your own wall or attic.

What about safety and building code?

Spray foam kits release chemical vapor while they cure: follow the kit’s instructions for respirator, protective clothing, ventilation and how long to stay out. Building codes generally require foam plastics to be covered by a thermal barrier or, in some places, an ignition barrier; check your local code and the kit’s listing. This calculator counts material only.

Spray Foam Insulation Calculator: How Many Board Feet and Kits Do I Need?

Board feet = square feet × inches of thickness, and kits = the board feet with waste ÷ the board feet on one kit, rounded up. For 40 ft of wall 8 ft high (320 sq ft) sprayed 2 in thick with closed-cell foam (about R-12), that is 640 board feet; with 15% for waste and overspray it is 736, or 2 kits of 650 board feet. A kit’s board feet are the maker’s nominal yield for a 1 in layer, so a thicker layer covers less area, and a real job rarely reaches the label figure: the waste allowance is an estimate, not a maker figure.

Figures based on the sources listed belowUpdated 2026-10-11How we calculate

Length (or total wall length)

Width (or wall height)

Waste and overspray

Careful, smooth open cavities (10%)Typical DIY, framing and some overspray (15%)Rough surfaces, rafters, wind or a first job (25%)Custom

Size the foam byWalls: enter the total wall length and the wall height. Attic or roof: enter the length and width of the surface you spray (the sloped area for a roof deck).

Foam thickness (in)

The finished thickness you want. Board feet = sq ft × inches. Kits are sprayed in thin layers (lifts), so check your kit’s maximum thickness per pass.

Foam typeSets the typical R per inch. DIY kits such as Froth-Pak and Touch ’n Seal are mostly closed-cell foam; open-cell kits exist at a lower density.

R per inch on your data sheet, or 0 for the typical figure

Makers state their own R-value (Froth-Pak lists about 6.2 per inch aged). Type your product’s figure for an exact R-value; leave 0 to use the typical figure for the foam type.

Kit sizeNominal board feet, which the makers state for a 1 in layer under ideal conditions. Real yield is usually lower: the waste setting covers the difference.

Board feet on your kit, or 0 to use the size above (board feet)

For another kit or a refill, type the board feet its box states.

Price per kit (optional)

Buy 2 kits

320 sq ft + 15% waste = 368 sq ft

Foam thickness: 2 in
Achieved R-value: R-12 (6 per inch, closed-cell)
Board feet of foam in place: 640 board feet
Board feet to buy (with waste and overspray): 736 board feet

How this number is calculated

320 sq ft + 15% waste = 368 sq ft ÷ 325 sq ft per kit = 2 kits

Shopping list

Full-face respirator with organic vapor cartridges
Disposable coveralls
Nitrile gloves (chemical resistant)
Safety goggles
Plastic sheeting
Foam trimming knife
Thickness gauge probe

Show diagram

Saved projects

No saved projects yet.

Board feet and coverage by thickness

Worked by this calculator for 100 sq ft (10 × 10 ft) of closed-cell foam, with 15% for waste and overspray. R-values use the typical 6.0 per inch (closed-cell) and 3.6 per inch (open-cell). A kit sprays its nominal board feet ÷ the thickness in sq ft, before waste.
Thickness	R-value (closed / open)	Board feet per 100 sq ft	With 15% waste	Sq ft per 650 board foot kit	Sq ft per 200 board foot kit
0.5 in	R-3 / R-1.8	50	58	1,300	400
1 in	R-6 / R-3.6	100	115	650	200
1.5 in	R-9 / R-5.4	150	173	433	133
2 in	R-12 / R-7.2	200	230	325	100
3 in	R-18 / R-10.8	300	345	217	67
4 in	R-24 / R-14.4	400	460	163	50
5.5 in	R-33 / R-19.8	550	633	118	36

Kits of 650 board feet by area and thickness

Whole kits with 15% waste and overspray, worked by this calculator. The nominal yield is a 1 in lab figure; a real job may differ, so keep a spare if the area is close to a whole kit.
Area	1 in	2 in	3 in	4 in
100 sq ft	1	1	1	1
250 sq ft	1	1	2	2
500 sq ft	1	2	3	4
1,000 sq ft	2	4	6	8
2,000 sq ft	4	8	11	15

Thickness for a target R-value

Thickness = target R-value ÷ R per inch, rounded up to the next 1/4 in (typical 6.0 closed-cell and 3.6 open-cell; the R-value reached is in brackets). Use your data sheet’s R per inch for an exact figure, and your climate zone and code for the target.
Target R-value	Closed-cell	Open-cell
R-13	2.25 in (R-13.5)	3.75 in (R-13.5)
R-19	3.25 in (R-19.5)	5.5 in (R-19.8)
R-21	3.5 in (R-21)	6 in (R-21.6)
R-30	5 in (R-30)	8.5 in (R-30.6)
R-38	6.5 in (R-39)	10.75 in (R-38.7)

Kit sizes and the area each sprays

Nominal board feet are the makers’ yields for a 1 in layer; the sq ft a kit sprays at a given thickness is the board feet ÷ the inches, before waste.
Kit	Sq ft at 1 in	Sq ft at 2 in	Sq ft at 3 in
200 board feet (Froth-Pak 200, Touch ’n Seal 200)	200	100	67
600 board feet (Touch ’n Seal 600)	600	300	200
650 board feet (Froth-Pak 650)	650	325	217

Methodology & assumptions

The area is the length × the width you enter (the total length of the wall × its height, or the length × width of an attic floor or the sloped area of a roof deck) less any openings. Board feet = area in sq ft × thickness in inches, because one board foot is 1 sq ft sprayed 1 in thick (144 cu in). The area is then increased by the waste allowance (10%, 15% or 25%: estimates for overspray, trimming, uneven surfaces and the gap between a kit’s lab yield and a real job, not manufacturer figures) and the kits are counted from the sq ft one kit covers: the kit’s nominal board feet ÷ the thickness, rounded up to whole kits. Kit sizes: 200 board feet (Froth-Pak 200, Touch ’n Seal 200); 600 board feet (Touch ’n Seal 600); 650 board feet (Froth-Pak 650). The makers state those yields for a 1 in layer under ideal conditions (Revchem’s Froth-Pak information sheet says theoretical yields are lab figures calculated at 1 in thick and that actual coverage will be lower in the field), which is why a waste allowance is built in. For any other kit, type the board feet on its box. R-value = thickness × R per inch. The typical figures are 6 per inch for closed-cell foam and 3.6 per inch for open-cell foam, from the U.S. Department of Energy’s Building America spray foam guide; makers publish their own values (Froth-Pak lists about 6.2 per inch aged), and the figure you type always wins. Given a target R-value, the thickness is the target ÷ R per inch, rounded up to the next 1/4 in so the layer is not short. The calculator counts a full single layer of one foam; it does not model foam over existing insulation, air-sealing-only work or thin sealing coats. Closed-cell and open-cell kits differ in density, price and maximum pass thickness: follow the kit’s data sheet for how thick each pass may be, and your local building code for thermal and ignition barriers over foam plastic. The figures are material counts, not a design. The metric toggle shows lengths in m, areas in m² and the thickness in cm.

DuPont (Froth-Pak), Froth-Pak 650 Spray Foam Insulation Kit product page: about 650 board feet, R-value 6.2 aged and 6.7 initial
DuPont (Froth-Pak), Froth-Pak 200 Sealant Spray Foam Kit product page: about 200 board feet
Revchem Composites, Froth-Pak Product Information Sheet: theoretical yields are lab figures calculated at 1 in thick; actual coverage will be lower
DAP, Touch ’n Seal Spray Foam Kit 200 Low GWP product page (200 board feet at a 1 in layer)
General Insulation Company, Touch ’n Seal U2-600 Spray Foam Insulation Kit listing (600 board feet at a 1 in layer, 1.75 lb density closed-cell foam)
U.S. Department of Energy, Building America, Spray Foam Guide: typical R-value about 3.6 per inch for open-cell and about 6 per inch for closed-cell spray polyurethane foam
ENERGY STAR, Recommended Home Insulation R-Values: the U.S. Department of Energy climate-zone table of R-values for attics, floors and walls; this page links to it and does not copy its numbers
The 10%, 15% and 25% waste allowances are rules of thumb of this calculator, not manufacturer figures; the R per inch of other products varies, so check the data sheet

How to calculate spray foam insulation

Measure the area. For walls, add up the length of the walls and multiply by the height. For an attic floor or the underside of a roof deck, multiply the length by the width (the sloped width for a roof). Subtract doors and windows.
Choose the thickness or the target R-value. Type the thickness you want, or the R-value for your climate zone and code (see the ENERGY STAR table in the sources) and the calculator works out the thickness from the foam type.
Pick the foam type and the kit. Closed-cell is about R-6 per inch and open-cell about R-3.6 per inch. Pick the kit size, or type the board feet printed on your kit’s box and the R per inch from its data sheet.
Add waste and divide. Multiply the area by the thickness for the board feet, add 10% to 25% for waste and overspray, and divide by the board feet on one kit. Round up to whole kits.
Spray in passes and check the depth. Follow the kit’s maximum thickness per pass, let each pass cure as the data sheet says, and check the finished depth with a probe against the thickness you planned.

Worked examples

Project	Result
40 ft of wall 8 ft high, closed-cell 2 in thick (about R-12), 650 board foot kits, 15% waste	320 sq ft, 640 board feet (736 with waste) → 2 kits
60 ft of wall 8 ft high less a door and two windows, closed-cell to R-13 (2.25 in), 600 board foot kits	435.99 sq ft, 1,129 board feet with waste → 2 kits
Rim joist band 9.25 in high all round a 30 × 40 ft house (140 ft), closed-cell 2 in, 200 board foot kits	107.8 sq ft, 248 board feet with waste → 2 kits
Roof deck, two sloped faces of 30 × 14 ft (840 sq ft), closed-cell to R-20 (3.5 in), 650 board foot kits	840 sq ft, 3,381 board feet with waste → 6 kits
40 × 8 ft wall, open-cell to R-19 (5.5 in), 650 board foot kits, 10% waste	320 sq ft, 1,936 board feet with waste → 3 kits
The first wall with a data sheet that says 6.2 per inch: R-value reached	320 sq ft, R-12.4 → 2 kits
The first wall with a kit whose box says 120 board feet	320 sq ft, 736 board feet with waste → 7 kits

Frequently asked questions

What is a board foot of spray foam?: One square foot sprayed one inch thick, which is 144 cubic inches (12 × 12 × 1 in), the same board foot lumber is sold by. So board feet = square feet × inches: 100 sq ft at 3 in is 300 board feet, and the same 300 board feet covers 150 sq ft at 2 in.
How many spray foam kits do I need?: Work out the board feet, add waste, and divide by the board feet on one kit. A 40 × 8 ft wall (320 sq ft) at 2 in is 640 board feet, 736 with 15% extra, which is 1.13 of a 650 board foot kit, so 2 kits. Without the extra it is 0.98 of a kit, so 1 kits. Kits come whole, so a small shortfall means another kit.
Why does a kit cover less than its label says?: Kit makers state the board feet for a 1 in layer under ideal conditions (Revchem’s Froth-Pak information sheet says theoretical yields are lab figures and that actual coverage will be lower). Cold chemical or surfaces, an uneven spray, overspray and trimming all use foam. That is what the waste setting is for: 10%, 15% and 25% are this calculator’s own estimates, so adjust them to your skill and conditions, or buy a spare kit.
Open-cell or closed-cell foam?: Per inch, closed-cell foam insulates about 6 against 3.6 for open-cell (U.S. DOE Building America figures), so it reaches a given R-value in about 60% of the thickness. For R-13, closed-cell takes 2.25 in and open-cell 3.75 in. Closed-cell is the denser foam and open-cell the lighter. Most DIY two-component kits, including Froth-Pak and Touch ’n Seal, are closed-cell, with open-cell kits also sold. Other sources quote slightly different ranges (about 3.5 to 3.8 open-cell, about 6 to 7 closed-cell), so use your product’s data sheet when you have it.
How thick should spray foam be?: Thick enough for your target R-value, within what the building and the product allow. Divide the target by R per inch: closed-cell R-13 is 2.25 in and R-19 is 3.25 in at 6 per inch. The R-value to aim for depends on your climate zone and the part of the house; ENERGY STAR hosts the U.S. Department of Energy table (linked in the sources), and this page does not copy its numbers. Kits are sprayed in thin passes, so a thick layer is built up in several lifts; follow the kit’s data sheet for the maximum per pass.
Do I subtract the studs or joists?: Foam is sprayed on the whole surface and covers the framing it touches, so the area is the wall or roof as measured. Subtract only doors, windows and other openings you will not spray. If you only fill the cavities between studs, the board feet are the cavity area × the depth; the extra on the framing faces is what the waste setting covers.
Can I use this for a roof deck or an unvented attic?: Yes for the quantity: enter the length and width of the underside of the roof deck (the sloped area, not the attic floor), pick the thickness or the R-value, and read the board feet and kits. Whether the design is allowed, and the thickness it needs, is a code and building-science matter, as is the attic ventilation: see the attic ventilation calculator and ask your local building department before you spray.
How does this compare with batts or blown-in?: Foam is counted in board feet and kits; batts and blown-in are counted in bags by the square feet or the bags per 1,000 sq ft on the package. Use the insulation calculator for the bag counts, and compare on R-value and cost for your own wall or attic.
What about safety and building code?: Spray foam kits release chemical vapor while they cure: follow the kit’s instructions for respirator, protective clothing, ventilation and how long to stay out. Building codes generally require foam plastics to be covered by a thermal barrier or, in some places, an ignition barrier; check your local code and the kit’s listing. This calculator counts material only.

Handy tools

Board Foot Calculator: The same unit: a board foot is 144 cu in, 12 × 12 in and 1 in thick, for lumber as for foam.
Feet and Inches Calculator: Turn a tape reading in feet, inches and fractions into the decimal feet the length and width take.