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Shed Insulation Calculator
Quick answer: Add up the four wall areas (perimeter times height), add the ceiling if you are insulating it, subtract doors and windows, reduce for framing, add waste and divide by the coverage on the package. That gives a package count for a 10×12, 12×24 or any rectangular shed. Check the shed's framing depth before choosing a product.
How it works
Walls = 2 × (length + width) × height. Ceiling = length × width (flat-ceiling estimate; sloped roofs have more area). Net = (walls + ceiling − openings) × (1 − framing %). Packages = net × (1 + waste %) ÷ coverage. Sheds are often framed with 2×4s, so cavities fit 3.5 in batts; thicker products get compressed. Sheds can trap moisture, so plan ventilation and a vapour control approach suited to your climate. Electrical work and any permits for a heated or occupied shed are separate; check local rules.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 12 × 10 ft shed, 8 ft walls, ceiling included, 30 sq ft of door and window, 10% framing, an assumed 40 sq ft per package, 5% waste. Walls = 352, ceiling = 120, gross 472 − 30 = 442. Net = 397.8. Packages = 397.8 × 1.05 ÷ 40 = 10.4, round up to 11.
FAQ
Batts or rigid foam?
Batts are simple between studs; rigid foam suits shallow framing. See compare.
Do I need a vapour barrier?
It depends on climate and use; ask a local building official.
What about a 12×24 shed?
Enter 24 and 12; the formula is the same.
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