Insulation Calculator
Work out how many rolls or bags of insulation you need from the area and the coverage per package.
Results are estimates for planning. Coverage varies by product and R-value — always check the figure printed on the package you're buying.
How to Measure for Insulation
Insulation is estimated from the area you want to cover and how much area each package handles.
Area to insulate
Measure the attic, wall, or floor area in square feet — or enter the length and width and let the calculator work it out.
Coverage per package
Every roll, batt bundle, or bag of blown-in insulation lists a coverage figure in square feet at a target R-value. Enter that number from the product label.
Common Mistakes to Avoid
- Guessing the coverage. Coverage differs a lot between products and R-values — read it off the package you're actually buying.
- No trim allowance. Batts get cut to fit around framing and obstacles; a small waste margin avoids a second trip.
- Compressing insulation. Squeezing batts into a tight space lowers the R-value — buy the right thickness instead.
- Adding a second vapor barrier. When topping up an attic, use unfaced insulation so moisture isn't trapped.
Frequently Asked Questions
Divide the area to insulate by the coverage on each package, round up, and add a little for trimming.
Each package lists the square feet it covers at a given R-value. Enter that figure into the calculator.
It depends on climate and location — attics often want R-38 to R-60, walls R-13 to R-21. Check your local energy code.
Packages are rated by gross area, so using the full area with a small waste allowance is safe.
Yes, in an attic — use unfaced insulation so you don't add a second vapor barrier and trap moisture.