Insulation Calculator
Work out how many rolls or batts of insulation you need for a wall or ceiling area, minus doors and windows.
Rolls / batts
1rolls
Net area
82ft²
Coverage per roll depends on both R-value and stud spacing — a higher R-value means a thicker batt that covers less area per package, so always confirm the exact figure on your product's label.
How the insulation calculator works
Insulation coverage is calculated the same way as paint or siding: find the net area you need to cover (wall area minus openings), then divide by how much a single roll or batt covers.
Formula: net area = (length × height) − (doors × 20) − (windows × 12). Rolls needed = net area ÷ coverage per roll, rounded up.
Coverage per roll isn't a fixed number — it changes with R-value and stud spacing, which is why it's a field you set yourself rather than a hardcoded constant. Check the roll's label for the exact square footage.
Frequently asked questions
It depends on both the R-value and your stud spacing. An R-13 batt sized for standard 16-inch on-center framing covers roughly 88 sq ft per roll, while the same R-value cut for 24-inch spacing covers closer to 135 sq ft — check the exact figure printed on your product's packaging.
R-value comes from thickness — roughly R-3.2 per inch for standard fiberglass batts. A higher R-value batt is thicker, so a package holds less total square footage of material even though it weighs about the same.
This calculator subtracts 20 sq ft per door and 12 sq ft per window, standard estimating figures for framed openings that won't be insulated the same way as open wall cavity.
This version is built around roll and batt insulation, which is sold and coverage-rated per package. Blown-in and spray foam use very different coverage math (based on bag yield at a target thickness) and aren't covered here yet.