Construction Calculator - Walls and Finishes

Insulation Calculator

Estimate insulation area, bags, and total R-value.

Reviewed: August 26, 2026

Calculate Insulation

For the Insulation Calculator, enter surface area, bag or batt coverage, r-value per inch, installed thickness, and waste allowance. It converts area and product coverage into whole insulation units and multiplies R-value per inch by thickness for a nominal layer R-value.

Construction measuring tools arranged beside a residential building project

Formula used

Material R-value = R per inch × installed thickness; package count = ceil(waste-adjusted area ÷ package coverage)

Insulation Calculator measurement plan showing Surface area square feet, Bag or batt coverage square feet / unit, R-value per inch R / inch

Worked insulation example

Insulation Calculator example: 602 ft² × 1.1 = 662.2 ft² of order coverage, or 17 units at 40 ft² each. 3.5 per inch × 6 in = R-21 material value.

Turn area into a material list

Round to whole bags, batts, or rolls and compare the simple material R-value with the assembly R-value required by the project.

Layout details outside the area formula

Compression, framing thermal bridges, gaps, settling, wind washing, moisture, installation grade, and product test value affect assembly performance.

Questions specific to this calculation

Why should product coverage and R-value come from the label?

Enter insulated surface area, package coverage, stated R-value per inch, installed thickness, and an allowance. Keep cavities with different depth or product separate.