Insulation calculator
Works for batts and rolls, or blown-in fiberglass and cellulose. Enter your attic or wall area to get packages or bags needed.
Area & material
How this is calculated
For batts and rolls, the area to cover (length × width) is increased by a 10% margin for cuts around joists, wiring, and odd corners, then divided by how much square footage one package covers — that number is on the package label and depends on the batt's R-value and thickness. For blown-in insulation, depth matters more than package count: area is multiplied by your target depth (converted from inches to feet) to get cubic feet, the same 10% margin is added, and the total is divided by the bag's cubic-foot yield, which is also printed on the bag and changes with the R-value you're blowing to.
How deep should attic insulation be?
Roughly 10–11" of blown-in fiberglass gets you to R-38, and 13–14" gets closer to R-49, which is the recommended level for most northern US climates. Check your local building code or a DOE climate zone map for the exact target where you live.
Batts or blown-in — which is better for an attic?
Blown-in fills irregular spaces and gaps around joists more completely and is faster to install over a large open attic floor. Batts are easier to fit precisely between studs in walls or a floor with obstructions you want to work around by hand.
Do I need to remove old insulation first?
Not usually — you can generally add new insulation, batts or blown-in, directly on top of old fiberglass or cellulose as long as it's dry and not damaged. Just add the new layer's depth to your target rather than starting from zero.
Once you know how much to order
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R-38 fiberglass batt, covers 88 sq ft
Matches the default package coverage above.
View on Home DepotLoose-fill fiberglass, 30 cu ft bag
Matches the default bag yield above — needs a blowing machine, often free to rent with bulk bag purchase.
View on Home DepotRespirator & coverall kit
Fiberglass particles are a real irritant — worth the few extra dollars.
View on Home Depot