# How much spray foam do I need?

Computes the board feet of spray foam insulation for an area and thickness, with extra for waste, how many kits to buy, and the R-value of open-cell or closed-cell foam.

- Page: https://www.acalculator.org/construction/spray-foam-calculator
- JSON spec: https://www.acalculator.org/construction/spray-foam-calculator.json
- Version: d1469cbfbfed

## Default answer

Example with the default inputs (Area to cover 500 ft², Thickness 2 in, Foam type Closed-cell, Extra for waste 10%, Kit yield (board feet) 600): Buy 1,100 bd ft of spray foam (kits: 2) for about R-12.6.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| a | Area to cover | The wall, roof or floor area to spray, openings left out. |
| t | Thickness | How thick the foam is sprayed. |
| foam | Foam type | Open-cell (about R-3.7 per inch), closed-cell (about R-6.3 per inch), or your product’s own R per inch. |
| r | R-value per inch | The R-value per inch on your foam’s label or data sheet. |
| extra | Extra for waste | Foam to add for overspray and uneven thickness. |
| kit | Kit yield (board feet) | The board feet one kit or set covers, from its label: for example 200 or 600. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| boardFeet | Board feet to buy | Area (ft²) × thickness (in) × (1 + extra ÷ 100). |
| netBoardFeet | Board feet sprayed | Area (ft²) × thickness (in), no extra. |
| kits | Kits | Board feet to buy ÷ kit yield, rounded up. |
| rValue | R-value | R per inch × thickness in inches. |
| cubicFeet | Volume (ft³) | Board feet ÷ 12. |
| cubicMeters | Volume (m³) | The foam volume to buy in cubic meters. |

## Method

Board feet = area (ft²) × thickness (in); to buy = board feet × (1 + extra ÷ 100); kits = to buy ÷ kit yield, rounded up; R-value = R per inch × thickness (in).

## Assumptions

- A board foot of foam is 1 ft² sprayed 1 in thick (144 in³).
- Closed-cell foam is R-6.3 per inch and open-cell R-3.7 per inch, from DOE’s Building America figures (3 in closed-cell is R-19, 7.5 in open-cell R-28); your product’s label may differ.
- The extra for waste covers overspray and uneven thickness; 10% by default.

## Worked examples

1. a = 46.45152, t = 0.0508, foam = closed, extra = 10%, kit = 600 gives boardFeet = 1,100, netBoardFeet = 1,000, kits = 2, rValue = 12.6, cubicFeet = 91.666667, cubicMeters = 2.595711. Source: US DOE Building America Solution Center, Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck: 3 in of closed-cell spray foam is R-19 and 7.5 in of open-cell spray foam is R-28, https://basc.pnnl.gov/resource-guides/unvented-conditioned-attic-spray-foam-insulation-below-roof-deck (retrieved 2026-10-18); NIST SP 811 (2008), Appendix B: 1 ft = 12 in, 1 in = 2.54 cm exactly.
2. a = 111.483648, t = 0.1397, foam = open, extra = 0%, kit = 600 gives boardFeet = 6,600, kits = 11, rValue = 20.35. Source: US DOE Building America Solution Center, Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck: 3 in of closed-cell spray foam is R-19 and 7.5 in of open-cell spray foam is R-28, https://basc.pnnl.gov/resource-guides/unvented-conditioned-attic-spray-foam-insulation-below-roof-deck (retrieved 2026-10-18).
3. a = 20, t = 0.05, foam = custom, r = 7, extra = 0%, kit = 200 gives boardFeet = 423.776001, kits = 3, rValue = 13.779528, cubicMeters = 1. Source: NIST SP 811 (2008), Appendix B: 1 ft = 12 in, 1 in = 2.54 cm exactly.

## FAQ

### How do I calculate board feet of spray foam?

Multiply the area in square feet by the thickness in inches. A board foot is 1 ft² sprayed 1 in thick, so 500 ft² at 2 in is 500 × 2 = 1,000 board feet. Add about 10% for overspray: 1,100 board feet.

### How many spray foam kits do I need?

Divide the board feet by the kit’s yield and round up. Kits are sold by the board feet they cover, often 200 or 600. 1,100 board feet ÷ 600 = 1.83, so buy 2 kits of 600.

### What R-value does spray foam give?

Multiply the R-value per inch by the thickness. DOE’s Building America Solution Center shows 3 in of closed-cell foam as R-19 and 7.5 in of open-cell foam as R-28, about R-6.3 and R-3.7 per inch, so 2 in of closed-cell is about R-12.6. Use your product’s label value if you have it.

### Should I use open-cell or closed-cell foam?

Closed-cell foam has about 1.7 times the R-value per inch and, at normal thickness, slows water vapor, but it costs more per board foot. Open-cell foam is lighter and cheaper, stops air, and lets water vapor through. Check what your building code and climate need.

### How thick should spray foam be?

It depends on the R-value your building code asks for. For R-13, closed-cell foam needs about 13 ÷ 6.3 = 2.1 in, and open-cell about 13 ÷ 3.7 = 3.5 in.

### How do I convert board feet to cubic feet?

Divide by 12. A board foot is 144 cubic inches, and a cubic foot is 1,728 cubic inches, so 1,200 board feet is 100 ft³ (2.83 m³).

## Sources

- US Department of Energy, Building America Solution Center (PNNL), Unvented Conditioned Attic with Spray Foam Insulation Below Roof Deck: 3 in of closed-cell spray foam is R-19 and 7.5 in of open-cell spray foam is R-28 (divided by the thickness: R-6.33 and R-3.73 per inch, shown as 6.3 and 3.7). https://basc.pnnl.gov/resource-guides/unvented-conditioned-attic-spray-foam-insulation-below-roof-deck (retrieved 2026-10-18)
- NIST SP 811 (2008), Appendix B: 1 ft = 12 in, 1 in = 2.54 cm exactly, so 1 ft² = 0.09290304 m² and 1 ft³ = 0.028316846592 m³. https://www.nist.gov/pml/special-publication-811 (retrieved 2026-10-18)