Attic Insulation Calculator
Attic floor area — the same as the house footprint under the roof. Most of the US wants R-38 to R-49 in the attic; if there is existing insulation, add batts to reach the target R-value (R-19 over R-19 ≈ R-38). Bag counts for every R-value are on the ticket.
Order 11 R-13 bags — bag coverage is printed on the bag — divide the square feet to cover by it for any product.
- Area
- 1,000 ft²
- Waste / cuts 5%
- + 50 ft²
- Coverage to buy
- 1,050 ft²
- Metric
- 92.9 m²
- R-13 kraft batts, 15″ × 93″ (≈ 97 ft²/bag)
- 11
- R-15 batts, 15″ × 93″ (≈ 68 ft²/bag)
- 16
- R-19 batts, 15″ × 93″ (≈ 49 ft²/bag)
- 22
- R-30 batts, 15″ × 48″ (≈ 58 ft²/bag)
- 18
- R-38 batts, 15″ × 48″ (≈ 43 ft²/bag)
- 25
- Materials + delivery$45–$85 / bag · Sep 2026
- $495 – $935
- Installed (with labor)typ. $1,660
- $995 – $2,685
Quantities follow the ticket. Links may earn us a commission at no cost to you; they never change a number.
What will this insulation job cost?
See the installed price range for these quantities and get up to 3 quotes from local contractors. Free, no obligation.
How to calculate insulation by hand
Bags = Area (ft²) × (1 + waste) ÷ coverage per bag (from the bag label)
Worked example
- Wall area: 40 ft × 8 ft = 320 ft²; with 5% waste, 336 ft².
- R-13 at 96.9 ft² per bag: 336 ÷ 96.9 = 3.5 → 4 bags.
- R-19 (2×6 walls) at 48.9 ft² per bag: 7 bags.
- Attic at R-38 (42.7 ft² per bag): 8 bags for the same 320 ft².
- 2×4 wall
- R-13 or R-15 (3½″)
- 2×6 wall
- R-19 or R-21 (5½″)
- Attic, most of the US
- R-38 to R-49
- Batt width
- 15″ for 16″ o.c. · 23″ for 24″ o.c.
Questions crews ask
How many bags of insulation for a 1,000 sq ft attic?
At R-38 batts (42.7 ft² per bag) with 5% waste: 25 bags. At R-30: 18 bags. Blown-in cellulose to R-38 needs about 26 bags of 25 lb; blown fibreglass about 20 bags — the depth chart on the bag is the authority.
How thick should attic insulation be?
About 12″ of fibreglass batts or 10–13″ of blown cellulose for R-38; 15–16″ for R-49. If you can see the joist tops you are well under R-30. Do not compress batts to fit — they lose R-value.
Can I lay new batts over old attic insulation?
Yes — use unfaced batts laid perpendicular to the joists over the existing layer. Faced batts on top trap moisture. Add up the R-values: existing R-19 plus new R-19 gives R-38.