Spray Foam Insulation Calculator — ft, sq ft, cost
How to use this calculator
Choose foam type, enter the surface area (or wall length × height), set target thickness or target R-value, and specify the cavity depth. The calculator computes board feet (1 bf = 1 ft² at 1″ thick), kits needed, R-value achieved, and whether a separate vapor barrier is required.
Open-cell — R-3.7/in, 0.5 lb/ft³. Needs separate vapor barrier.
Closed-cell — R-6.5/in, 2.0 lb/ft³. Acts as vapor barrier at ≥ 2″ thick.
Saved Calculations
| Time | Type | Area ft² | Thick | BF | Kits | R-Value | Cost |
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How to Calculate Spray Foam Insulation
Spray foam insulation is measured in board feet (bf). One board foot = 1 ft² of coverage at 1″ thick. Multiply the surface area by the thickness in inches to get the total board feet. Spray foam comes in kits rated by board feet: 200, 600, and 1,200 bf are common sizes.
Formulas
Board feet = area (ft²) × thickness (in). From R-value: thickness = target R / R-per-inch. Open-cell: R/in = 3.7, density 0.5 lb/ft³. Closed-cell: R/in = 6.5, density 2.0 lb/ft³. Weight = area × (thickness/12) × density.
FAQ
Open vs closed cell? Open-cell is cheaper, expands more, good for sound dampening, but needs a vapor barrier. Closed-cell is denser, stronger, acts as its own vapor barrier at ≥2″, and provides higher R-value per inch.
How thick should I spray? For walls: open-cell 3–5.5″ (fills 2×4 or 2×6 cavity), closed-cell 1–3″. For attics: open-cell 5.5–10″, closed-cell 3–5″.
