How this calculator works
It divides the area you’re insulating by the square footage each bag of blown-in or pack of batts covers — printed on the package for your chosen R-value.
Worked example — a 30 ft × 25 ft attic, 40 sq ft per bag:
750 sq ft ÷ 40 = 19 bags.
750 sq ft ÷ 40 = 19 bags.
Coverage drops with R-value
Higher R-values mean a thicker layer, so each bag covers less area. Always read the coverage chart on the bag for the R-value you want and enter that figure.
Frequently asked questions
How do I know how many bags of insulation I need?
Divide the area by the coverage-per-bag for your target R-value, which is listed on the bag.
What R-value do I need for an attic?
Most regions call for R-38 to R-60 in attics — check your local code.