Insulation Calculator
Divides net wall area by the coverage printed on an R-13 batt for 2×4 walls (often about 40 sq ft per batt).
Step 1: Units
Step 2
Enter project measurements
Use decimals if needed (e.g. 3.5).
Step 3
How to use this calculator
Adjust mentally if you use high-density batts with different coverage.
What the math is doing
Batt count = ceil((sq ft × (1+waste)) ÷ 40).
Frequently asked questions
24 in o.c. framing?
Batt widths change; verify SKU coverage.
Vapor retarder facing?
Climate zone dictates placement side.
Sound batts?
Densities differ; counts still start from area ÷ coverage.
Electrical?
Split batts around boxes carefully.