Insulation Calculator
How many bags or batts to buy from square footage and the label coverage. Click any i for detail.
Coverage
Area (sq ft)
i
Area
Attic floor or wall cavity area you will cover. |
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|---|---|
Coverage per bag/batt (sq ft)
i
Coverage
Read the bag. Blown attics often list a range by R-value; unfaced R-13 15-in batts are often ~32–40 sq ft per bag depending on brand. |
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Waste (%)
i
Waste
Cuts, odd cavities, and settling. 10% is a common adder. |
How to use this calculator
- Enter the area.
- Copy coverage sq ft from the product you will buy.
- Add waste.
- Ceil at the register.
Results explained
Need = area × (1 + waste%). Units = ceil(need ÷ coverage). Blown-in and spray-foam cost pages price labor; this page answers how many bags.
Quick reference: insulation count
Always use the bag’s coverage at your target R — charts vary.
| Item | Detail |
|---|---|
| Label coverage | Primary input |
| R-30 blown attic | Often ~32–40 sq ft/bag — check bag |
| 15-in R-13 batt bag | Brand-dependent |
| Spray foam dollars | See spray-foam insulation cost |
Vapor retarders and baffles are not in the count.
How the estimate is built
units = ceil(area × (1 + waste%) ÷ coverage).
Example scenario
1,200 sq ft, 40 sq ft/bag, 10% waste → 1,320 / 40 = 33 bags.
FAQ
Blown vs batt?
Same division. Change coverage to the product.
Cost of blown-in?
Use the blown insulation cost calculator.
Wall vs attic?
Cavity area vs floor area — measure the surface you will fill.