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Spray Foam Insulation Calculator

Calculate board feet of open-cell or closed-cell spray foam for an area and thickness, the number of DIY kits or drum sets, the R-value (and metric RSI) and the foam volume.

Units

Area to spray (m² or ft²)

Foam type

Thickness

Kit or set size

Waste and overspray

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How it works

board feet = area (ft²) × thickness (in) × (1 + waste) · kits = board feet ÷ kit yield (rounded up) · R = R per inch × thickness · RSI = R × 0.1761 · 1 m² = 10.764 ft²

Spray polyurethane foam is sold by its theoretical yield in board feet — one square foot one inch thick. Multiply the area in square feet by the thickness in inches and add 10–15% for overspray and uneven cavities. Closed-cell foam (about 2 lb/ft³) gives roughly R-6 to R-7 per inch and also acts as an air and vapour barrier; open-cell foam (about 0.5 lb/ft³) gives about R-3.5 to R-3.8 per inch and is cheaper per board foot (US Department of Energy). Kit yields are nominal at ideal temperatures; cold tanks and surfaces can cut yield by a third.

Worked example

Spraying 100 m² (1,076 ft²) with 2″ of closed-cell foam and 10% waste: 1,076.4 × 2 × 1.1 = 2,368 board feet, so 2,368 ÷ 600 = 3.9 → 4 kits of 600 board feet. The layer reaches R-13 (RSI 2.29) and is 5.08 m³ of foam.

Sources: US Department of Energy — Insulation materials (sprayed foam) · Spray Polyurethane Foam Alliance

Frequently asked questions

What is a board foot of spray foam?

One square foot of foam one inch thick (144 cubic inches). A 600 board-foot kit covers 600 ft² at 1″, 300 ft² at 2″ or 200 ft² at 3″.

Open-cell or closed-cell spray foam?

Closed-cell gives about twice the R-value per inch, adds rigidity and blocks vapour — good for basements, rim joists and metal buildings. Open-cell is cheaper, softer and better for sound and for roof decks in dry climates.

How thick should spray foam be?

Common targets are 2–3″ of closed-cell in walls (R-13 to R-20), 3.5″ of open-cell to fill a 2×4 wall (about R-13), and 5.5–10″ of open-cell or 3–5″ of closed-cell under roofs, depending on climate zone.

How many square metres does a 600 board-foot kit cover?

About 55.7 m² at 1″ (2.5 cm), 27.9 m² at 2″ and 18.6 m² at 3″ — less in cold conditions.

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This calculator is for educational purposes. Double-check important results before acting on them.