Formula
How the insulation estimate works
- Net surface area = surface length × surface height − openings
- Target coverage = net surface area × (1 + waste %)
- Packages required = target coverage ÷ coverage per package, rounded up
Free project planning tool
Insulation calculator
Estimate insulation coverage, full packages, purchased area, waste, and material cost.
✓ Metric & imperial✓ Transparent assumptions✓ No signup
Batts & packagesInstant estimate
Example calculation
A 30 × 8 ft wall with 32 sq ft of openings has 208 sq ft to cover. With 10% waste and 40 sq ft per package, the purchase quantity rounds up to six packages.
Planning tips
- Use the coverage printed on the actual batt, roll, or bag package.
- Calculate walls, ceilings, and different cavity depths separately.
- Confirm the required R-value, vapor control, and local code before buying.
Common questions
Insulation calculator FAQ
Does this choose the correct R-value?
No. It estimates quantity only. Required R-value depends on climate, assembly, cavity depth, and local building requirements.
Should I subtract windows and doors?
Yes, when you want a tighter material estimate. Keep a waste allowance for cuts, damaged pieces, and awkward cavities.
Can I use it for blown insulation?
Use the area result as a starting point, then follow the manufacturer’s bag-coverage chart for the target depth and R-value.
Planning guides
Understand the estimate
01Estimating checklistA repeatable checklist for measuring a project, verifying product coverage, rounding packages, pricing the order, and reviewing the result.→02Material waste allowanceChoose a waste allowance based on cuts, breakage, patterns, package sizes, and project complexity instead of one universal percentage.→03Methodology & assumptionsHow BuildWise calculators handle measurements, units, product coverage, waste, package rounding, cost, examples, and limitations.→