Insulation Calculator
Bags = attic area ÷ 1,000 × bags per 1,000 ft² on the bag chart. A 1,000 ft² uninsulated attic in zone 5 needs R-60: 31.5 AttiCat bags per 1,000 ft², so 32 bags blown 20.5 in deep. With 3 to 4 in already there, ENERGY STAR asks less on top: R-49 in zone 5, 25 bags.
AttiCat bags for R-60
32 bags
1,000 ft² at 31.5 bags per 1,000 ft², rounded up; blow at least 20.5 in
- ENERGY STAR, zone 4C, 5 and 6, uninsulated attic
- add R-60
- Minimum thickness
- 20.5 in
- Bags per 1,000 ft²
- 31.5
Blow every bag over the area and reach the minimum thickness: either one short lowers the R-value (Owens Corning).
Checked by the Yardstick Math team · How we check
Worked examples
A 1,000 ft² attic in zone 5, no insulation
- ENERGY STAR, zone 5, uninsulated attic: R60
- AttiCat R-60 line: 31.5 bags per 1,000 ft², 20.5 in minimum
- 1,000 ÷ 1,000 × 31.5 = 31.5, rounded up to 32
Result: 32 bags of AttiCat, blown at least 20.5 in deep.
Checked by the automated test “insulation — 1,000 ft² attic in zone 5, uninsulated → R-60 → 31.5 bags per 1,000 ft² → 32 bags, 20.5 in”.
The same attic in square meters
- 100 m² = 1,076.4 ft²
- AttiCat R-49 line: 25 bags per 1,000 ft²
- 1,076.4 ÷ 1,000 × 25 = 26.9, rounded up to 27
Result: 27 bags for R-49 on 100 m².
Checked by the automated test “insulation — metric: 100 m² = 1,076.4 ft² at R-49 → 26.9 → 27 bags”.
How it works
R-value to add = ENERGY STAR attic level for your climate zone (uninsulated, or 3–4 in already there)
Bags = attic area ÷ 1,000 ft² × bags per 1,000 ft² for that R-value, rounded up
Depth = minimum thickness printed for that R-value
Assumptions
- ENERGY STAR attic levels: zone 1 R30 (R25 over 3–4 in), zones 2 and 3 R49 (R38), zones 4 to 8 R60 (R49).
- Default product: Owens Corning AttiCat, December 2025 data sheet; a value between two lines (R-25) is counted at the next line up (R-26).
- Another product: type the bags per 1,000 ft² and the minimum thickness printed on its bag for your R-value.
- The area is the attic floor, length × width; nothing is deducted.
Reference table
| R-value | Bags per 1,000 ft² | Minimum thickness, in (mm) |
|---|---|---|
| R-13 | 5.9 | 5 (127) |
| R-19 | 9 | 7 (178) |
| R-22 | 10.5 | 8 (203) |
| R-26 | 12.6 | 9.5 (241) |
| R-30 | 14.6 | 10.75 (273) |
| R-38 | 19 | 13.5 (343) |
| R-44 | 22.4 | 15.5 (394) |
| R-49 | 25 | 17 (432) |
| R-60 | 31.5 | 20.5 (521) |
AttiCat only: another blown-in product has its own chart on the bag.
Before you start
- Find your zone. ENERGY STAR sets the R-value by climate zone; zone 4C is grouped with 5 and 6.
- Measure the floor. Length × width of the attic floor, in square feet or square meters.
- Read the bag. Owens Corning: the stated R-value needs the required number of bags at no less than the minimum thickness on the label.
Common mistakes
- Buying inches instead of R-value The depth for an R-value depends on the product: AttiCat reaches R-30 at 10.75 in. Pick the R-value first, then read the depth on the bag.
- Ignoring what is already there With 3 to 4 in in place, ENERGY STAR asks R-49 on top in zone 5 instead of R-60: 25 bags instead of 32 on 1,000 ft².
- Using another product's chart The chart on this page is AttiCat's: for another blown-in product, count with the chart printed on the bag you buy.
- Using the national chart in Minnesota Owens Corning adds bags and inches for Minnesota code: at R-60, 4.9 more bags per 1,000 ft² and 2.5 more inches, so 37 bags and 23 in on 1,000 ft².
- Stopping at the depth or at the bag count Owens Corning: installing fewer bags than the chart, or less than the minimum thickness, gives a lower R-value. Check both.
Frequently asked questions
How much insulation do I need?
Find your climate zone (1 to 8): ENERGY STAR asks, for an uninsulated attic, R30 in zone 1, R49 in zones 2 and 3, R60 in zones 4 to 8. On 1,000 ft², R-60 takes 32 bags of AttiCat.
What R-value do I need in the attic?
ENERGY STAR: R30 to R60 for an uninsulated attic depending on the zone, or R25 to R49 on top of 3 to 4 in already there.
How many bags of blown-in insulation do I need?
Area ÷ 1,000 × the bags per 1,000 ft² printed for your R-value: 1,200 ft² at R-49 with AttiCat (25 per 1,000 ft²) takes 30 bags.
How thick is R30 insulation?
It depends on the product, there is no single depth: AttiCat blown-in reaches R-30 at 10.75 in minimum, 15 bags on 1,000 ft². Another product prints its own depth on the bag.
How thick is R38 or R49 insulation?
With AttiCat blown-in: R-38 at 13.5 in minimum (19 bags per 1,000 ft²), R-49 at 17 in (25 bags). Another product prints its own depths on the bag.
Sources
Formula, examples and sources checked on by the Yardstick Math team. How we check our formulas.
- Recommended Home Insulation R-Values — ENERGY STAR (U.S. EPA), accessed
- AttiCat Blown-In PINK Fiberglas Insulation, Product Data Sheet — Owens Corning, accessed
- AttiCat Expanding Blown-In PINK Fiberglas Insulation, Fact Sheet (Pub. 10011287-E) — Owens Corning, accessed