Spray Foam Insulation Calculator — m, m², 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 coverage in m² at the given thickness, kits needed, thermal resistance (R-value), U-value, and whether a separate vapour barrier is required.
Open-cell — λ=0.038 W/mK, density 8 kg/m³. Needs separate vapour barrier.
Closed-cell — λ=0.022 W/mK, density 32 kg/m³. Acts as vapour barrier at ≥ 50 mm.
Saved Calculations
| Time | Type | Area m² | Thick | Kits | R-Value | Cost |
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How to Calculate Spray Foam Insulation (Metric)
Spray foam insulation coverage depends on the surface area and application thickness. The thermal resistance R = thickness / λ (thermal conductivity). Kit sizes are rated by coverage at a reference thickness (typically 50 mm). Divide actual thickness by 50 mm to get the coverage reduction factor.
Formulas
R-value = thickness(m) / λ. U-value = 1 / R. Volume = area × thickness. Weight = volume × density. Open-cell: λ=0.038 W/mK, ρ=8 kg/m³. Closed-cell: λ=0.022 W/mK, ρ=32 kg/m³. Kit coverage at target thickness = rated coverage × (50 / target thickness mm).
FAQ
Open vs closed cell? Open-cell is cheaper, good for sound dampening, but needs a vapour barrier. Closed-cell is denser, stronger, acts as its own vapour barrier at ≥ 50 mm, and provides better thermal performance per mm.
What U-value should I target? Walls: U ≤ 0.30 W/m²K (well-insulated). Roofs: U ≤ 0.20. Floors: U ≤ 0.25. Check local building regulations for specific requirements.
