Insulation Calculator

Estimate blown-in cellulose bags or batt counts for a target R-value, with the coverage assumption stated on the page.

Worked example

An attic of 50 m² insulated to R-50 with blown-in cellulose. Coverage per bag = 3.7 × (40 ÷ 50) = 2.96 m². Bags = 50 ÷ 2.96 = 16.9, rounded up to 17 bags. Depth is about 270 mm × (50 ÷ 40) = 338 mm. R-50 equals RSI 8.8.

How it works

Labelled assumption: a typical 28.5 kg bag of blown-in cellulose covers about 3.7 m² at R-40, based on manufacturer coverage charts. Coverage scales inversely with R-value: coverage at your target = 3.7 × (40 ÷ target R). Bags = area ÷ coverage, rounded up. Blown depth at R-40 is about 270 mm and scales in proportion to R. RSI = R ÷ 5.678. Batt mode simply divides the area by the area of one batt and rounds up; it does not adjust for the batt's own R-value, so match the batt product to your target R separately.

FAQ

What R-value should I target in a Canadian attic?
Many provinces target roughly R-50 (RSI 8.8) or higher for attic insulation in new construction, but requirements vary by province and municipality. Treat this as guidance and check your local building code.

Does this work for fibreglass batts?
The bags figure is cellulose-specific. Use batt mode for batts of any material; it counts pieces by area only, so confirm the batt package's stated R-value meets your target.

Estimates only. Mississippi Maple provides approximate material estimates for planning. Coverage varies by product and installation; verify quantities with your supplier or contractor before purchasing, and check local building code requirements.