Calculators · Insulation Calculator
InteriorInsulation Calculator
Enter your area to get the batts, rolls or blown-in bags to buy. See the ENERGY STAR R-value for your climate zone.
Packages needed
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How to calculate how much insulation you need
Insulation is sold by the package or the bag, and both cover a known area. Start with the area you want to insulate, then divide by what one unit covers.
| Step | Formula |
|---|---|
| 1. Area of each surface | rectangle: length × width. Triangle: base × height ÷ 2 |
| 2. Net area | total area − windows, doors and other openings |
| 3. Area with extra | net area × (1 + extra ÷ 100) |
| 4a. Batts and rolls | area with extra ÷ coverage per package, rounded up |
| 4b. Blown-in bags | area with extra ÷ 1,000 × bags per 1,000 sq ft, rounded up |
The calculator reads measurements typed like 10'6" or 10 ft 6 in and accepts feet, inches, yards and meters. Use “Add another area” for each wall, ceiling or gable end and the total updates as you type. If you only know the size of one piece, the coverage of a package is width × length ÷ 144 × pieces, with width and length in inches.
Example 1: batts for a wall
A wall measures 30 ft by 8 ft and has 50 sq ft of windows and a door. You want 10% extra. The batts come in packages of 12 pieces, each 15 in by 93 in.
| Step | Operation | Result |
|---|---|---|
| Wall area | 30 × 8 | 240 sq ft |
| Net area | 240 − 50 | 190 sq ft |
| With 10% extra | 190 × 1.10 | 209 sq ft |
| One piece | 15 × 93 ÷ 144 | 9.6875 sq ft |
| One package | 12 × 9.6875 | 116.25 sq ft |
| Packages | 209 ÷ 116.25 = 1.80, rounded up | 2 packages |
Two packages cover 232.5 sq ft, so 23.5 sq ft is left over. The pieces needed are 209 ÷ 9.6875 = 21.57, so 22 pieces. The 15 in by 93 in size with 12 pieces appears on the Knauf EcoBatt fact sheet. The R-value of a package is on its label, so pick the one that fits your wall cavity.
ENERGY STAR R-values by climate zone
ENERGY STAR publishes the R-values it recommends when you add insulation to an existing wood-framed home. The table repeats them. The page says they are based on table R402.1.3 of the 2021 International Energy Conservation Code. We read it in October 2026 at energystar.gov, where you will also find the climate zone map.
| Zone | Attic, uninsulated | Attic, 3 to 4 in already | Floor |
|---|---|---|---|
| 1 | R-30 | R-25 | R-13 |
| 2 | R-49 | R-38 | R-13 |
| 3 | R-49 | R-38 | R-19 |
| 4A and 4B | R-60 | R-49 | R-19 |
| 4C, 5 and 6 | R-60 | R-49 | R-30 |
| 7 and 8 | R-60 | R-49 | R-38 |
For walls, the same ENERGY STAR page does not give a wall R-value. When siding is removed it suggests blowing insulation into an empty wall cavity and adding insulative sheathing of R-5 in zone 3 or R-5 to R-10 in zones 4 to 8. For a basement or crawlspace wall it lists R-5 sheathing or an R-13 batt in zone 3, R-10 sheathing or an R-13 batt in zones 4A and 4B, and R-15 sheathing or an R-19 batt in zones 4C and 5 to 8. This calculator does not choose wall products. It only counts the packages for the area you give it.
How many bags of blown-in insulation per 1,000 sq ft?
The manufacturers publish the bags needed for each R-value. The first product is the Owens Corning AttiCat PINK data sheet (May 2026, 27.5 lb bag). The second is the Johns Manville Attic Protector B-785 coverage card (January 2019). We read both in October 2026. Both say the stated R-value needs the minimum number of bags and at least the minimum thickness.
| R-value | Owens Corning bags per 1,000 sq ft | Min. thickness | Johns Manville bags per 1,000 sq ft | Min. thickness |
|---|---|---|---|---|
| R-19 | 9 | 7 in | 9.0 | 8.2 in |
| R-30 | 14.6 | 10.75 in | 14.9 | 12.4 in |
| R-38 | 19 | 13.5 in | 19.4 | 15.3 in |
| R-49 | 25 | 17 in | 25.9 | 19.1 in |
| R-60 | 31.5 | 20.5 in | 32.6 | 22.6 in |
Example 2: a 1,000 sq ft attic in zone 4A
An uninsulated attic of 25 ft by 40 ft in zone 4A. ENERGY STAR recommends R-60. With 10% extra the area to cover is 1,000 × 1.10 = 1,100 sq ft.
| Product | Operation | Bags |
|---|---|---|
| Owens Corning AttiCat, R-60 | 1.1 × 31.5 = 34.65, rounded up | 35 bags |
| Johns Manville Attic Protector, R-60 | 1.1 × 32.6 = 35.86, rounded up | 36 bags |
Both products also need a minimum installed thickness for R-60, 20.5 in for Owens Corning and 22.6 in for Johns Manville. A bag count alone does not give the stated R-value.
How many packages do I need?
This table uses a package that covers 116.25 sq ft, the 12-piece package of 15 in by 93 in batts. Divide the area by the coverage of your own package to check any row.
| Area | Packages (exact) | Packages to buy |
|---|---|---|
| 100 sq ft | 0.86 | 1 |
| 200 sq ft | 1.72 | 2 |
| 500 sq ft | 4.30 | 5 |
| 1,000 sq ft | 8.60 | 9 |
Tips for ordering
- Match the width of the batt to your framing. The Owens Corning EcoTouch data sheet (checked October 2026) lists 15 in and 23 in widths for wood framing and 16 in and 24 in widths for metal framing.
- For blown-in insulation, count the bags and also measure the depth after you blow it. Both numbers have to be met.
- Measure irregular spaces as several rectangles and triangles and add them with “Add another area”.
- Ask the supplier for the coverage of the exact package. Coverage changes with the R-value and the width.
Frequently asked questions
How do I figure how much insulation I need?
Measure the area in square feet, subtract openings such as windows and doors, and add a small allowance for cuts if you want one. For batts and rolls, divide that area by the coverage printed on one package and round up. For blown-in insulation, multiply the area in thousands of square feet by the bags per 1,000 square feet in the manufacturer table for your R-value, then round up.
How many square feet are in a roll or package of insulation?
It depends on the product, the width and the thickness, so read the coverage on the package. Knauf lists packages from 32 to 352 square feet on its EcoBatt fact sheet, for example 12 pieces of 15 by 93 inches covering 116.25 square feet. If you only know the size, multiply width by length in inches, divide by 144 and multiply by the pieces in the package.
How much blown-in insulation do I need for 1,000 square feet?
It depends on the R-value you want. For R-49, Owens Corning lists 25 bags of AttiCat per 1,000 square feet at a minimum thickness of 17 inches, and Johns Manville lists 25.9 bags at 19.1 inches. For R-30 the figures are 14.6 and 14.9 bags. The calculator uses those tables and rounds up to whole bags.
How many inches of blown-in insulation is R-30?
The two manufacturer tables we checked in October 2026 give different numbers because the products differ. Owens Corning AttiCat needs a minimum installed thickness of 10.75 inches for R-30, and Johns Manville Attic Protector needs 12.4 inches. Use the thickness and the number of bags together, as the manufacturers require both.
What R-value does ENERGY STAR recommend for an attic?
For adding insulation to an existing wood-framed home, ENERGY STAR gives R-30 to R-60 for an uninsulated attic depending on the climate zone, and R-25 to R-49 if you already have 3 to 4 inches. Choose your zone in the calculator to see the exact value. The numbers are based on the 2021 IECC.
Should I add extra for waste?
A little extra covers cuts and trimming around framing, but the right amount depends on the job and your installer. Type the percentage you want in the extra box and the calculator adds it to the area before it counts packages or bags. Leave it empty to add nothing.
How much does insulation cost per square foot?
Prices change by region, product and store, so this calculator does not show them. Take the number of packages or bags from the result and ask local suppliers for a quote in the same unit.
Insulating with foam instead? Use the spray foam insulation calculator to get board feet and kits. Nothing you type leaves your browser.
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