Insulation Calculator
Find the required insulation thickness and volume for a target R-value.
Assumptions used in this calculation
- Ideal installation: Uses the material's nominal, lab-tested R-value per inch, real-world performance drops with compression, gaps, or improper installation.
- No vapor barrier or air sealing accounted: Calculates insulation thickness only, it doesn't factor in the added performance of air sealing or vapor barriers, which also affect real-world energy efficiency.
About this calculator
Building codes specify a target R-value, a measure of thermal resistance, for attics, walls and floors, but converting that target into an actual, buyable thickness depends entirely on which insulation material you're using, since materials vary widely in how much resistance they pack per inch. This calculator divides your target R-value by the selected material's R-value per inch, spray foam is denser and reaches a target R-value in a much thinner layer than loose-fill fiberglass, to output the required thickness, and can extend that into total material volume across your area. Instead of looking up a material's R-value-per-inch rating and doing the division yourself, pick the material and enter your target R-value and area to get an installation-ready thickness figure immediately. It uses each material's nominal, lab-tested R-value; real-world performance drops with compression, gaps or improper installation, so proper installation technique matters as much as hitting the calculated thickness.
Worked example
500 sqft, R-30, fiberglass batt
Result: 8.57 in thick
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