Insulation Calculator
Calculate how many batts or rolls of insulation you need for walls, attics, or crawl spaces based on area and R-value.
ft
ft
sq ft
Rolls/Batts Needed
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Total Area —
Area to Order For —
How to Use This Calculator
- Enter the area length and width to insulate in feet.
- Select the target R-value.
- Enter the coverage per roll/bag from your product label.
- Results show rolls/batts needed with a 10% waste buffer.
Formula
Total area = Length × Width
Rolls needed = ceil(Total area × 1.10 ÷ Coverage per roll)
Example
Example: 40×30 ft attic, R-38, 40 sq ft per roll → 1,200 sq ft → 33 rolls (with 10% waste).
Frequently Asked Questions
- R-values vary by climate zone. Attics typically need R-38 to R-60; walls need R-13 to R-21; floors need R-25 to R-30. Check ENERGY STAR recommendations for your zone.
- A batt is a pre-cut piece of insulation (typically 16 or 24 inches wide, 4 or 8 feet long). Rolls are the same product in longer continuous lengths.
- Coverage depends on the R-value and product. Check the coverage chart on the bag — it lists square feet per bag for each R-value.
- Measure the attic floor area (length × width). Enter the target R-value to see bags or rolls needed.
- Add 10% to account for cutting around joists, pipes, and other obstructions.