Insulation Calculator
Building envelope and product coverage
Enter surfaces, openings, and insulation coverage
Result
Calculation summary
Enter values to see the result
Insulation coverage preview
Attic insulation
How to use this calculator
- 1Choose an attic, wall, floor, or combined project and enter the measured dimensions.
- 2For wall projects, add doors, windows, or custom openings that will not receive insulation.
- 3Select the material form, enter the target R-value and coverage printed for one package or unit, then calculate.
Formula
Units = ceil(((gross area − applicable wall openings) × (1 + waste ÷ 100)) ÷ coverage per unit)
Openings are deducted only from wall regions. Package coverage must be the manufacturer-stated coverage at the selected product and target R-value.
Calculation steps
- Validate all region, opening, material, coverage, R-value, unit, and waste inputs.
- Convert every rectangular region into square meters and combine the gross areas.
- Subtract door and window area from wall regions without reducing attic or floor area.
- Apply the waste allowance to the net insulation area.
- Divide by the user-entered coverage per package or unit and round up.
Worked example
A 10 m × 8 m attic has 80 m² of area. With 10% waste and 10 m² coverage per package at the chosen R-value, the adjusted area is 88 m² and the estimate rounds up to 9 packages.
Assumptions
- Every region and opening is rectangular and uses finished measured dimensions.
- Openings are deducted only from wall regions and cannot make wall area negative.
- The target R-value is recorded for planning and does not automatically select a code requirement or material thickness.
- Coverage per package or unit comes from the exact product label for the intended R-value, thickness, and installation method.
- Counts are rounded up; compression, framing, ventilation clearances, air sealing, vapor control, and local code requirements must be checked separately.
Sources
Frequently asked questions
Where should I find coverage per package?
Use the net coverage printed on the exact product package or technical data sheet at the R-value and thickness you plan to install.
Does the calculator recommend an R-value?
No. R-value requirements depend on climate, building assembly, project type, and local rules. Enter the target confirmed for your project.
Should I subtract doors and windows?
You can subtract openings from wall regions. Small openings may be left in the measured area when the extra material is useful for cuts and installation losses.
Can I calculate blown-in insulation?
Yes. Select loose fill and enter the square-area coverage per bag stated by the manufacturer for your target R-value or installed depth.
Does this include air sealing or vapor control?
No. The estimate covers insulation quantity only. Air sealing, ventilation, vapor control, fire safety, and installation details require separate planning.