Insulation Calculator
Estimate batt or roll insulation by the area you are covering. Coverage per bag depends on R-value; this assumes ~88 sq ft, common for R-13 wall batts.
Insulation calculator
How it's calculated: Length ft × width ft = square feet; add 5% waste and divide by the coverage per bag (about 88 sq ft for R-13 batts), rounding up.
How to estimate insulation
- Coverage per bag changes with R-value and width - a thicker, higher-R batt covers less. Check the package.
- Measure the actual area between framing you need to fill, not the gross wall or attic size.
- For attics, blown-in insulation is priced by bag-per-target-R-value instead; this estimator is for batts and rolls.
- Never compress batts to fit - squashing fiberglass cuts its R-value. Match the batt thickness to the cavity.
- Air-seal before you insulate: caulk and foam the gaps and penetrations first, because batts filter moving air rather than stop it.
Frequently asked questions
How much area does a bag of insulation cover?
It depends on R-value. R-13 wall batts often cover ~88 sq ft per bag; higher R-values cover less, so always check the label.
What R-value do I need?
It depends on climate and location in the house: walls commonly take R-13 (2x4 framing) to R-21 (2x6), while attics in cold climates often target R-49 or more. Your local code office publishes the targets for your zone.
Faced or unfaced batts?
Faced (kraft paper) batts install with the facing toward the heated living space, where the paper acts as a vapor retarder. Use unfaced for adding a layer on top of existing attic insulation or where a separate vapor barrier exists.
Are batts sized for stud spacing?
Yes - batts come in widths for 16 and 24 inch on-center framing. Buy the width that matches your framing so batts friction-fit without cutting, and only trim for odd bays.
Batts or blown-in for an attic?
Blown-in covers an open attic faster and fills gaps and odd spots better. Batts make sense in walls, accessible joist bays and anywhere you may need to lift insulation back out for access.