Batt Insulation Coverage & Bundle Calculator
How many batt bundles for your square footage? Divide the area by the coverage on the bag, add waste, round up.
Calculator
500 ft² at 88 ft²/bundle needs about 6 bundles — buy 7 with 10% waste. Batt coverage varies by width and R (e.g. R-13 3.5" ~88 ft², R-30 ~58 ft², labeled) — read the bag.
Batts are sold by the bundle, and each bundle covers a labeled square footage for its R-value and width. Buy by the bundle, not the batt: this tool takes your net area, adds a waste allowance for offcuts around framing and obstructions, and rounds up to whole bundles so you leave the store with enough.
The default sizes a 500 ft² 2×4 wall in R-13 kraft-faced batt (~88 ft² per bundle) with 10% waste.
Formula
bundles = ceil( area_sqft × (1 + waste%) ÷ coverage_per_bundle )
The ceil matters — you cannot buy 6.25 bundles, so it always rounds up to 7. Waste is applied to the area before rounding.
Worked example
500 ft² of 2×4 wall, R-13. With 10% waste: 500 × 1.10 = 550 ft²; 550 ÷ 88 = 6.25; round up to 7 bundles. Skip the waste and it is 500 ÷ 88 = 5.68 → 6 bundles — but that leaves nothing for the inevitable miscuts, so buy 7.
Background & practice
Coverage falls as R rises. A thicker, higher-R batt fits fewer square feet per bundle: R-13 ~88 ft², R-19 ~75 ft², R-30 ~58 ft², R-38 ~40 ft². Grab the number off the exact bag — do not reuse an R-13 figure for an R-30 order.
Faced vs unfaced. Kraft or foil facing is your vapor retarder; use it toward the heated side in cold climates, and use unfaced when you are adding a second layer over existing insulation (a second vapor retarder can trap moisture).
What to measure first: net area after openings, the stud/joist spacing (16″ vs 24″ o.c. changes batt width), and the cavity depth so you buy a batt that fills it without compressing. For a full wall with openings, use the wall insulation calculator instead.
Reference table
| Batt R-value | Coverage per bundle (labeled) | Bundles for 500 ft² | Bundles for 1,000 ft² |
|---|---|---|---|
| R13 | 88 ft²/bundle | 6 | 12 |
| R15 | 67 ft²/bundle | 8 | 15 |
| R19 | 75 ft²/bundle | 7 | 14 |
| R21 | 58 ft²/bundle | 9 | 18 |
| R30 | 58 ft²/bundle | 9 | 18 |
| R38 | 40 ft²/bundle | 13 | 25 |
Coverage per bundle drops as the batt gets thicker (higher R) — read the number printed on the bag and add ~5–10% for offcuts.