Spray Foam Thickness Calculator
How thick does the foam need to be?
Pick a foam, then enter the R-value you need or the depth you have. Every answer comes straight from the product's published IAPMO evaluation report — no rules of thumb, no multiplication.
Calculator
Enter a number, e.g. 38.
| Installed thickness | R-value |
|---|---|
| 1″ | R-4.1 |
| 3.5″ | R-13 |
| 4″ | R-14 |
| 5.5″ | R-20 |
| 7.5″ | R-27 |
| 9.5″ | R-34 |
| 11.5″ | R-42 |
| 14″ | R-51 |
| Installed thickness | R-value |
|---|---|
| 1″ | R-7.3 |
| 3.5″ | R-25 |
| 4″ | R-28 |
| 5.5″ | R-39 |
| 7.25″ | R-51 |
| 9.25″ | R-65 |
| 11″ | R-77 |
| 12″ | R-84 |
Values from Table 1 of each IAPMO Uniform Evaluation Service report, at a 75°F mean temperature. Required R-values depend on your climate zone and the code your jurisdiction has adopted — confirm them with your building official.
Compare with the 2021 IECC
Prescriptive minimums for houses from Table R402.1.3 of the 2021 International Energy Conservation Code. Your jurisdiction may use a different edition, local amendments or another compliance path, so treat this as a starting point and confirm with your building official.
Climate zones are assigned by county in IECC Figure R301.1 and Table R301.1. "ci" means continuous insulation; "R-13 + R-5 ci" means R-13 in the cavity plus R-5 continuous. For ceilings with attics, Section R402.2.1 lets R-38 satisfy an R-49 requirement, and R-49 satisfy R-60, where the full uncompressed depth extends over the wall top plate at the eaves. Thicknesses shown are the thinnest published in each product's IAPMO report that meet the cavity-only minimum.
Why doesn't the calculator just multiply R-value per inch by thickness?+
Because the evaluation reports don't. Each IAPMO report publishes a table of R-values calculated from tested k-factors at two thicknesses, and the results are not a straight line. ComfortSeal 500 gives R-4.1 per inch at 1 inch, falling to R-3.5 to R-3.7 per inch from 3.5 to 14 inches, so 3.5 inches is R-13, not the R-14.4 that multiplying would suggest. The R-value per inch of this insulation varies with thickness. The thicker the insulation, the lower the R-value per inch. The higher the R-value, the greater the insulating power. Ask your seller for the fact sheet on R-values. This tool uses the published table exactly.
What happens if I enter a thickness that isn't in the table?+
You can enter any number. In target mode the tool answers with the thinnest published thickness that meets or exceeds your R-value. In depth mode it answers with the published value at your depth; if that depth isn't published, it gives the nearest published value at or below it, or, below the first full thickness in the table, the two published points your depth falls between. It never interpolates, because the reports don't, and it shows the full table so you can see the neighbouring values.
Does this tell me what my local code requires?+
No. Required R-values depend on your climate zone, the code edition your jurisdiction has adopted and any local amendments. Check with your building official or design professional, then use this tool to find the thickness that meets it.
Which foam should I use?+
Open cell (ComfortSeal 500) suits interior walls, attic rooflines and sound control. Closed cell (ComfortSeal HFO) gives more R-value in the same depth and acts as a Class II vapor retarder at 2 inches, so it suits exterior walls, crawl spaces and humid climates.
Know your thickness? Get it sprayed.
Find a certified ComfortSeal installer, or talk to our team about supply.