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Spray Foam Insulation Calculator

Estimate the spray foam kit size needed based on area, cavity depth, and foam type.

Result

Kits Needed
2

A "board foot" equals 1 sq ft covered at 1 inch of thickness. Open-cell foam expands more and yields roughly 600 board feet per standard kit, while denser closed-cell foam yields roughly 200 board feet per kit for the same kit size.

About the Spray Foam Calculator

The Spray Foam Insulation Calculator estimates how many spray foam kits are needed to fill a wall, attic, or rim joist cavity to a target depth, based on the area covered and whether open-cell or closed-cell foam is used. Because the two foam types expand to very different yields, kit counts can differ substantially for the same square footage.

How It Works

You enter the area to cover, the cavity depth you need filled in inches, and select open-cell or closed-cell foam. The calculator multiplies area by depth to get total board feet needed, where one board foot is one square foot covered at one inch of thickness, then divides by the yield of a standard kit for the chosen foam type and rounds up to a whole kit.

Board feet needed = area (sq ft) x depth (in). Kits needed = ceiling(board feet needed / board feet per kit), using 600 board feet per kit for open-cell foam or 200 board feet per kit for closed-cell foam.

Examples

300 sq ft wall with open-cell foam

Filling 300 square feet to a 3.5 inch cavity depth with open-cell foam needs 1,050 board feet, which at 600 board feet per kit rounds up to 2 kits.

500 sq ft rim joist area with closed-cell foam

Filling 500 square feet to a 2 inch depth with denser closed-cell foam needs 1,000 board feet, which at 200 board feet per kit comes out to exactly 5 kits.

Advantages

  • Converts area and depth into board feet, the unit spray foam kits are actually rated in, so the estimate matches how the product is sold.
  • Keeps open-cell and closed-cell yield rates separate, since applying the wrong yield to the wrong foam type can significantly under-order material.
  • Rounds up to whole kits, reflecting that a partially used kit generally cannot be saved for a later job.

Common Mistakes

  • Assuming open-cell and closed-cell kits yield the same board footage, when open-cell typically covers about three times as much area per kit at the same depth.
  • Overlooking that board feet scale with depth, so filling a cavity twice as deep roughly doubles the kit requirement for the same area.
  • Not accounting for job-site temperature, since most spray foam kits need to be within a manufacturer-specified range to expand and yield as rated.

Edge Cases to Watch For

  • The result always rounds up to a whole kit, even for a small remainder, since an activated spray foam kit cannot be partially used and saved for another job.
  • The 600 and 200 board-foot yield figures are averages for standard kit sizes; actual yield varies by manufacturer and by the ambient temperature and humidity during application.
  • The calculator assumes one uniform fill depth across the whole area; cavities with mixed depths, such as varying rafter or stud dimensions, should be entered as separate calculations for an accurate total.

Common Use Cases

  • Insulation contractors quoting kit quantities for a rim joist, attic, or wall cavity spray foam job.
  • Homeowners pricing a spray foam kit for a smaller, self-installed project like a crawlspace or band joist.
  • Builders comparing open-cell versus closed-cell kit costs for a given cavity depth before specifying which foam to use.
Written & fact-checked by the Calculateus TeamLast updated August 5, 2026How we verify our formulas

Frequently asked questions

Why would someone choose closed-cell foam despite it covering less area per kit?

Closed-cell foam is significantly denser, providing a higher R-value per inch (roughly R-6 to R-7 versus roughly R-3.5 to R-4 for open-cell), adds structural rigidity to the wall assembly, and acts as its own vapor barrier and air seal - it's often chosen for thin cavities where maximum R-value per inch matters, or for below-grade and exterior applications where moisture resistance is important.

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Conclusion

Because spray foam kits are rated in board feet rather than square footage alone, this calculator's depth-aware math gives a more reliable kit count than a flat area-based guess. Check the yield rating printed on your specific kit's packaging, since it can vary somewhat from the standard figures used here.