Spray Foam Calculator
Estimate how many board feet and sets of open or closed cell spray foam a job needs from the area and depth, with the R-value you get. Measure walls, a roof deck or a total area; add your yield per set and a price to get the sets and the material cost.
Your numbers
Decimals: 5.5 for 5-1/2 in.
Typical aged values from the Building America guide. Use the figure on your product's data sheet.
Board feet one set gives. Typical: open cell 13,000 to 15,000, closed cell 4,000 to 5,000. Your product's data sheet or your own jobs beat these.
For the material cost of the job.
Board feet to spray, with waste
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- Sets
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- R-value
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- Area
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- Board feet before waste
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The calculation runs in your browser and ParrotNotes does not store your numbers. They sit in the page address so you can bookmark or share the result.
How spray foam is estimated
Spray foam is sold and bid in board feet: one square foot of foam one inch thick. Board feet = square feet × inches of depth. Add a waste allowance, then divide by what one set (the A side and B side drums used together) yields on your rig to get the number of sets to bring.
Worked example: a 1,000 sq ft attic roof deck with 5-1/2 inches of open cell is 5,500 board feet. With 10% waste that is 6,050 board feet; at 14,000 board feet a set it uses 0.43 of a set. At R-3.6 per inch it comes to about R-19.8.
Measuring walls and roof decks
For walls, measure the length of each wall and the height, multiply, and take off the windows and doors. For the underside of a roof deck, the sloped area is larger than the floor below it: multiply the building's length by its width, then by the pitch factor √(1 + (rise ÷ 12)²). A 6/12 roof is 1.118 times its footprint, a 12/12 roof 1.414 times. Gable ends and dormers are extra; add them as walls or square feet.
Foam sprayed between studs or rafters fills the cavity, not the framing, so the area of the wall slightly overstates the foam. The calculator does not take the framing off; the waste figure is where to adjust for it.
R-value and coverage by depth
At the page's defaults: R-3.6 per inch and 14,000 board feet a set for open cell, R-6.1 per inch and 4,500 board feet a set for closed cell, before waste. 3-1/2 and 5-1/2 inches are the depths of 2×4 and 2×6 stud cavities.
| Depth | Open cell R | Open cell sq ft a set | Closed cell R | Closed cell sq ft a set |
|---|---|---|---|---|
| 1 in | R-3.6 | 14,000 | R-6.1 | 4,500 |
| 2 in | R-7.2 | 7,000 | R-12.2 | 2,250 |
| 3 in | R-10.8 | 4,667 | R-18.3 | 1,500 |
| 3.5 in | R-12.6 | 4,000 | R-21.3 | 1,286 |
| 5.5 in | R-19.8 | 2,545 | R-33.6 | 818 |
| 7.25 in | R-26.1 | 1,931 | R-44.2 | 621 |
Open cell or closed cell
Open cell foam weighs about 0.5 lb per cubic foot and gives about R-3.6 per inch; closed cell weighs about 2 lb and gives about R-6.1. Closed cell takes much more chemical per board foot, which is why a set covers about a third as many board feet. The Building America guide also notes that closed cell is a vapor retarder at typical thicknesses and open cell is not, which matters in cold and hot-humid climates.
Both are combustible: the guide notes that the International Residential Code generally requires a thermal barrier over foam in living space, with ignition barrier exceptions for some attics and crawl spaces. Check the product's evaluation report and the local code for the maximum thickness and the barrier.
For insulation contractors and home services sales: what to write down
On the walk-through, note every area to spray with its dimensions, the depth or R-value the homeowner or the code wants, open or closed cell, what is in the way (wiring, ducts, old insulation to remove), access for the rig and hoses, and whether a barrier coating is needed. Read the numbers back before you leave, so the bid and the sets on the truck match the job.
Sources, each read on 2026-10-29. Results are estimates; the product's data sheet, its evaluation report and the local code govern:
- Spray Foam Systems: Calculating the amount of spray foam needed for a job (board feet, yield per set, 10% buffer)
- U.S. DOE Building America, Steven Winter Associates (CARB): Which Spray Foam Is Right For You? (2009): densities, R-value per inch, pass thickness, barriers
- Green Insulation Technologies, 2.0 Pound closed cell data sheet: yield 4,000 to 4,500 board feet, R-6.62 per inch aged, lift thickness
- Natural Polymers, Natural-Therm 0.50 open cell data sheet: R-3.7 at 1 inch, 1 to 6 inch lifts, what yield depends on
Quoting blown-in, batts or rigid foam board instead? The insulation calculator works out the R-value to add and the bags, bundles or sheets, and the roofing calculator the roof area from the pitch.
More for home services and building products sales: Home improvement sales, Building materials sales, HVAC sales training, Roofing sales training.
The job is measured on the walk-through
Wall lengths, roof pitch, what the homeowner wants sprayed and how thick all come up on the walk-through. Say them out loud and record the visit in ParrotNotes: you get a transcript, a summary and the action items, so the bid matches what you walked.
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