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Spray Foam Calculator
Quick answer: Spray foam is sold by board feet, where one board foot is one square foot one inch thick. Multiply area by thickness, add an overspray allowance, and divide by the kit's rated board-foot yield to get the number of kits. Closed-cell foam typically gives a higher R per inch than open-cell. Follow the maker's safety rules.
How it works
Board feet = area × thickness (in) × (1 + waste %). Kits = board feet ÷ kit yield. Nominal R = thickness × R per inch (typical: closed-cell about R6–7/in, open-cell about R3.5–3.7/in; your product label governs). Kit yields on labels are usually under ideal conditions; temperature, technique and substrate lower real yield. Two-component spray foam releases chemicals during application; the U.S. EPA and manufacturers advise ventilation, respiratory protection and keeping others away. Many homeowners hire certified installers for larger jobs; see DIY vs hire.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 200 sq ft rim joist and wall area, 2 in closed-cell at an assumed R6.5/in, an assumed 600 board-foot kit, 15% waste. Board feet = 200 × 2 × 1.15 = 460. Kits = 1 (0.77). Nominal R13.
FAQ
Open or closed-cell?
Closed-cell adds more R per inch and resists moisture; open-cell is softer and lower R. See compare.
Can I spray over old insulation?
Usually not; remove loose material first and never disturb vermiculite.
Do I need PPE?
Yes; see tools and PPE.
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