Insulation Calculator
Free insulation calculator. Enter the area and target R-value to get the required insulation thickness for fiberglass, rock wool, cellulose or spray foam, plus bundle count.
About This Free Online Insulation Calculator
Our free insulation calculator works out how thick your insulation needs to be to hit a target R-value, then estimates the number of bundles to cover your wall, ceiling or attic. Pick the material — fiberglass batts, rock wool, cellulose blown-in, closed-cell or open-cell spray foam — enter the area in square feet and your target R-value, and the tool returns the required thickness in inches, the total insulation volume, and a bundle count based on the coverage you enter. R-per-inch values are standard industry figures. Every calculation runs in your browser with no signup.
Features of Our Insulation Calculator
- Required thickness from target R-value and material
- Material-aware R-per-inch (fiberglass, rock wool, cellulose, foam)
- Bundle estimate from your product's coverage
- Total insulation volume in cubic feet
- Great for walls, attics, ceilings and rim joists
- 100% client-side and private — no signup, no data sent
How to Use the Insulation Calculator
Using this tool is simple and requires no signup or registration. Follow these steps:
- Pick your insulation material.
- Enter the area to insulate in square feet and the target R-value.
- Set the coverage per bundle from your product label.
- Read the required thickness and number of bundles.
Frequently Asked Questions About Insulation Calculator
How thick should my insulation be for R-30?
Thickness is R-value divided by the material's R-per-inch. Fiberglass batts (about 3.2 per inch) need roughly 9.4 inches for R-30, while closed-cell spray foam (about 6.5 per inch) needs only about 4.6 inches. This calculator applies the correct R-per-inch for each material.
What R-value do I need?
It depends on where you live and what you are insulating. Attics often call for R-38 to R-60, walls R-13 to R-23, and floors R-19 to R-30. Check your local building code for the required value, then enter it here.
How many bundles of insulation do I need?
Divide the area (with a waste allowance) by the coverage per bundle shown on the product label. Enter that coverage in the calculator and it returns the bundle count, rounded up, with your chosen waste margin.
Why do different materials need different thicknesses?
Each material resists heat at a different rate per inch. Spray foam has a high R-per-inch so it needs less depth; fiberglass and cellulose need more depth for the same R-value. The calculator accounts for this automatically.
Is this insulation calculator free?
Yes, completely free with no signup. Every estimate runs in your browser, so nothing is uploaded or tracked.
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