DIY Cost Tools
Insulation Calculator
Estimate insulation coverage, whole packages, waste, and material cost for a wall, floor, or attic surface. Enter the package coverage at the R-value you need.
Measure: Measure surface length and width, subtract large openings, and copy the package coverage at your target R-value.
How the estimate works: The calculator uses your measurements, unit conversions, waste allowance, and product coverage to create a planning quantity. Review the formula shown above, then read the matching guide below before ordering. See How Our Calculators Work for assumptions and limitations.
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How this calculator works
Insulation area = length × width − openings. Purchase area adds waste and is divided by the package coverage, rounded up.
Use the package coverage for your target R-value
The same insulation product can cover different areas at different installed depths. Copy the coverage shown for the R-value and application you need. Do not compress batts into a shallower cavity; compression changes thermal performance.
Safety and building checks
Air sealing, moisture control, ventilation, recessed-light clearances, combustion appliances, wiring, and local energy requirements can affect the project. Confirm the assembly before purchasing.
Read the complete insulation planning guide: area, packages, and r-value.
Insulation coverage example
A 40-by-24-foot rectangular room has a 128-foot perimeter. At 8 feet high, the gross exterior wall area is 1,024 square feet. Subtract 140 square feet of measured windows and doors to get 884 square feet, then add the chosen allowance. Package count must be based on the exact product’s printed coverage and the cavity size it is designed to fit.
Match the assembly, not only the area
Separate walls, ceilings, rim joists, sloped roofs, and floors because they may need different R-values, facing, vapor control, air sealing, and installation methods. Confirm stud or joist spacing, cavity depth, fire and ignition-barrier requirements, ventilation, recessed fixtures, moisture conditions, and local energy code. Compressed or poorly fitted insulation may not deliver its labeled performance.