This insulation calculator estimates how many rolls or batts you need to cover a wall, floor, or attic. Enter the area and the coverage per package above to get the number of packages, with a small allowance for trimming.
How to use this calculator
- Enter the area to insulate in square feet (length × width).
- Enter the coverage printed on the roll or batt package.
- Read how many packages you need.
How is insulation quantity calculated?
Area (ft²) = Length × Width Packages = Area ÷ Coverage per package × (1 + waste %)
- Coverage — square feet one roll or batt covers (from the label)
- Waste % — 5–10% for trimming and gaps
Example calculation
For a 1,000 ft² attic with rolls that cover 50 ft² each:
- Rolls = 1,000 ÷ 50 = 20
- Add 5% waste → buy 21 rolls
Match the R-value to your climate
- Attics: R-38 to R-60 in most US zones.
- Walls: R-13 to R-21 for 2×4 and 2×6 framing.
- Floors: R-25 to R-30 over unconditioned space.
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Frequently Asked Questions
How much insulation do I need?
Divide the area to cover by the coverage of one roll or batt. A 1,000 sq ft attic with 50 sq ft rolls needs about 20 rolls, plus a little extra for trimming.
What R-value do I need for an attic?
Most US attics target R-38 to R-60 depending on climate zone. Check your local building code, as colder zones require higher R-values.
Should I add extra for waste?
Yes, add about 5 to 10 percent for trimming around joists, pipes, and edges, and round up to whole packages.