How much insulation do I need?

Divide the area you are insulating by the coverage per bag (on the product label) and add a small waste allowance. Enter your numbers above.

How many square feet does a bag of insulation cover?

It varies by R-value and product — a bag of batts typically covers 40–90 square feet. Use the figure printed on your product.

Does the calculator account for R-value?

No — the coverage per bag already reflects the R-value you picked, so enter the coverage for the specific product you are buying.

Insulation Calculator

Work out how many bags of insulation you need. Enter the area to insulate and the coverage per bag from the product label to get the number of bags, with a waste allowance.

Insulation calculator

Enter the coverage per bag from the product label — it already reflects the R-value you chose. Add a small waste allowance for trimming around studs and obstructions.

How it's calculated

We divide the area by the coverage per bag and add a waste allowance, rounding up to whole bags. The coverage figure already reflects your chosen R-value, so it comes straight from the product.

Frequently asked questions

How much insulation do I need?: Divide the area you are insulating by the coverage per bag (on the product label) and add a small waste allowance. Enter your numbers above.
How many square feet does a bag of insulation cover?: It varies by R-value and product — a bag of batts typically covers 40–90 square feet. Use the figure printed on your product.
Does the calculator account for R-value?: No — the coverage per bag already reflects the R-value you picked, so enter the coverage for the specific product you are buying.

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<iframe id="hmc-insulation-calculator" src="https://howmanycalc.com/embed/insulation-calculator/" title="Insulation calculator by HowManyCalc" width="100%" height="520" style="border:1px solid #e4e8ec;border-radius:12px;max-width:680px" loading="lazy"></iframe>
<p style="font:12px sans-serif">Insulation calculator by <a href="https://howmanycalc.com/insulation-calculator/">HowManyCalc</a></p>
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Last updated June 2026.