Insulation Calculator
You need your area divided by the coverage per bag at your target R-value. Enter the area and the coverage printed on the bag to get the number of bags and the cost.
How to estimate insulation bags
Measure the area you are insulating — usually the attic floor or wall surface — then divide by the coverage per bag at your target R-value. That coverage is printed on every bag and drops as the R-value rises, so use the figure for the exact product you are buying.
Target R-values
Insulation is rated by R-value, its resistance to heat flow. Attics typically need R-38 to R-60, walls R-13 to R-21, depending on your climate zone. The higher the target, the thicker the layer and the fewer square feet each bag covers.
After insulating
Once the cavities are filled, board over them — size the panels with the drywall calculator. For irregular gable walls, total the area with the square footage calculator.
Frequently asked
How many bags of insulation do I need?
Divide the area you are insulating by the coverage per bag at your target R-value. The coverage shrinks as the R-value rises, so always read it from the bag you plan to buy.
What R-value do I need?
Attics commonly target R-38 to R-60 depending on climate zone, while walls run R-13 to R-21. Higher R-value means more material per square foot.
How does coverage change with R-value?
A bag of blown-in insulation might cover 60 sq ft at R-19 but only 30 sq ft at R-49, because you apply it thicker. The bag label lists coverage for each R-value.