Insulation calculator
Estimate the cavity area to fill with batt or roll insulation and the packages to buy, from wall or ceiling dimensions with framing, or from a count of cavities.
Surface length and height up to 1,000 m, 1 to 100,000 cavities with widths up to 2 m and lengths up to 100 m, framing spacing up to 2 m, member thickness up to 0.5 m, framing share from 0 to 90%, package coverage up to 1,000 m², 1 to 1,000 pieces per package up to 3 m wide and 30 m long, and allowance from 0 to 50%. Calculated on your device; download a JSON report and a results CSV. This calculator uses the measurement fields only. Results update as you type. Up to 1,000,000 characters.
Your result
How to use Insulation calculator
- Enter the wall or ceiling dimensions and openings, or the number and size of cavities.
- Describe the framing with its spacing and thickness, or enter a framing percentage.
- Enter the coverage per package, or the pieces per package and their size.
- Review the cavity area, packages and surplus, then download the JSON report or the CSV.
Useful next steps
Cavity area
Studs and joists take up part of every wall and ceiling, and that lumber blocks space that could hold insulation (Building America Solution Center, Advanced Framing: Minimum Wall Studs, PNNL, checked 16 October 2026). The calculator takes the surface after openings and removes the framing share: 1.5 in members at 16 in centres take 1.5 ÷ 16 = 9.375%, so a 40 × 8 ft wall has 290 ft² of cavity.
Framing share
Spacing and thickness count only the evenly spaced studs or joists. Plates, headers, blocking and extra studs at corners and openings add more framing, so if you have measured or been given a framing percentage, enter that instead. Counting cavities directly, each with its clear width and length, avoids the question.
Packages
Coverage per package is the insulation face area in one package: pieces × width × length, or the figure you enter. Packages are rounded up after the extra allowance. If you are unsure whether a label means the insulation area or the wall area at a framing spacing, use the pieces and piece size option.
Limits
The calculator does not choose an R-value, check an energy code or cover vapour control, fire stopping or loose-fill depth. Unit conversions use NIST SP 811.