How do I calculate how much insulation I need?

Measure the area (wall height × length, or attic length × width), deduct framing for batts, add a little waste, and divide by the coverage printed on the bag for your target R-value.

How many bags of blown-in insulation do I need?

Divide attic area by the bag's coverage at your target R-value. Coverage per bag falls as R-value rises, so always use the manufacturer's chart.

Free tool

Insulation calculator

Bags of batts or blown-in for walls and attics, from area and your bag's coverage.

Inputs

Area to insulate (SF)TypeFraming spacingCoverage per bag (SF, from bag)Waste %

Estimated materials

Bags: 29 bags
Net area to fill: 1,134 SF
Framing deducted: 10%

Coverage per bag depends on the product and R-value — read it off the bag's coverage chart (e.g. an R-13 batt bag often covers ~40 SF; blown-in coverage drops as target R-value rises). Estimate — verify before ordering.

Frequently asked

How do I calculate how much insulation I need?: Measure the area (wall height × length, or attic length × width), deduct framing for batts, add a little waste, and divide by the coverage printed on the bag for your target R-value.
How many bags of blown-in insulation do I need?: Divide attic area by the bag's coverage at your target R-value. Coverage per bag falls as R-value rises, so always use the manufacturer's chart.

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