Insulation Calculator
How many rolls or batts of insulation a wall or ceiling takes, with doors and windows subtracted and coverage set by your R-value and stud spacing.
Rolls / batts
1rolls
Net area
82ft²
Coverage per roll depends on R-value and stud spacing together. A higher R-value is a thicker batt, and a thicker batt covers less ground per package, so confirm the figure on your label before ordering.
How the insulation calculator works
Insulation works like paint or siding. Find the net area you have to cover, which is wall area minus the openings, then divide by how much one 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 is not a fixed number. It moves with R-value and stud spacing, so it is a field you fill in instead of a constant baked into the calculator. The exact square footage is on the label.
Wondering whether now is a good time to buy? The Insulation Price Index tracks the federal price index for building insulation, which has been falling while most materials climb.
Frequently asked questions
It depends on the R-value and your stud spacing, which is why there is no single answer. An R-13 batt cut for 16-inch on center framing covers roughly 88 sq ft per roll. The same R-value cut for 24-inch spacing covers closer to 135. The real figure is printed on the package, so use that one.
R-value comes from thickness, roughly R-3.2 per inch for standard fiberglass. A higher R-value batt is a thicker batt, and a package only holds so much volume, so you get fewer square feet in a bag that weighs about the same. Upgrading R-value quietly increases the number of packages you need.
20 sq ft per door and 12 sq ft per window. Those are standard estimating figures for framed openings, which do not take cavity insulation the way an open stud bay does. They are averages, so measure anything unusually large yourself.
Rolls and batts, which are sold with a coverage rating per package. Blown-in works off bag yield at a target depth instead, and there is a separate Blown-In Insulation Calculator for that. Spray foam is a third calculation again, estimated by kit yield, and is not covered here.
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