Insulation calculator
How much insulation to buy: bags of blown-in for your attic at the R-value your climate calls for, batts for walls, or board feet of spray foam.
You need
25 bags
- Area
- 1,000 sq ft
- Chart row
- R-49
- Minimum depth
- 17.00 in.
- Foam thickness
- 17.00 in.
- Board feet
- 0
- Estimated cost
- That's past the bag chart. Blow to the chart's top row, or check the chart on the bag you buy.
ENERGY STAR suggests adding R-49 to the attic in Zone 4A or 4B, and R-19 under floors. Bags are the maker's minimum per 1,000 sq ft for that R-value; blow at least the minimum depth too. Your target falls between chart rows, so this uses the next row up. Use the chart printed on the bag you buy. Pick batts to fit the framing depth; enter the square feet on the bag to count bags. Thickness uses DOE's typical R per inch; products vary, so check the data sheet. Spray foam is often installed by a contractor.
How much insulation do I need?
Start with the R-value to add, from the ENERGY STAR table for your climate zone, and the area: the attic floor, or the wall or floor you're insulating. Then:
- Blown-in: find the R-value on the bag's coverage chart (or the next row up). Bags = area ÷ 1,000 × bags per 1,000 sq ft, rounded up, blown to at least the chart's minimum depth.
- Batts or rolls: bags = area ÷ square feet per bag on the label, rounded up.
- Spray foam: thickness = R-value ÷ R per inch (about 3.6 for open-cell, 6 for closed-cell); board feet = area × thickness in inches.
Worked example
A 1,000 sq ft attic in Zone 4A or 4B with 3–4 in. already there: ENERGY STAR suggests adding R-49. On the Owens Corning AttiCat PINK, 27.5 lb bag chart, R-49 takes 25.0 bags per 1,000 sq ft, so 1,000 ÷ 1,000 × 25.0 = 25 bags, blown at least 17.00 in. deep. The same job with Greenfiber INS541LD, 19.05 lb bag takes 84 bags at 13.68 in. settled.
Recommended R-values by climate zone
From ENERGY STAR, Recommended Home Insulation R-Values (2021 IECC Table R402.1.3), for adding insulation to existing wood-framed homes. Your local code may ask for more on new work.
| Zone | Attic, none now | Attic, 3–4 in. now | Floor |
|---|---|---|---|
| Zone 1 | R-30 | R-25 | R-13 |
| Zone 2 | R-49 | R-38 | R-13 |
| Zone 3 | R-49 | R-38 | R-19 |
| Zone 4A or 4B | R-60 | R-49 | R-19 |
| Zone 4C, 5 or 6 | R-60 | R-49 | R-30 |
| Zone 7 or 8 | R-60 | R-49 | R-38 |
Blown-in bags per 1,000 sq ft
From the bag charts: Owens Corning AttiCat PINK Blown-In product data sheet (Pub. No. 10011273-L, May 2026) and Greenfiber INS541LD blow-in cellulose attic card (PM-6.3-194 Rev F 03/15). Bag weights and charts change, so use the one on your bag.
| R-value | Fiberglass bags | Min. depth | Cellulose bags | Settled depth |
|---|---|---|---|---|
| R-13 | 5.9 | 5.00 in. | 17.9 | 3.86 in. |
| R-19 | 9.0 | 7.00 in. | 27.2 | 5.57 in. |
| R-22 | 10.5 | 8.00 in. | 32.2 | 6.41 in. |
| R-25 | – | – | 37.2 | 7.25 in. |
| R-26 | 12.6 | 9.50 in. | – | – |
| R-30 | 14.6 | 10.75 in. | 46.1 | 8.62 in. |
| R-38 | 19.0 | 13.50 in. | 61.1 | 10.77 in. |
| R-44 | 22.4 | 15.50 in. | – | – |
| R-49 | 25.0 | 17.00 in. | 83.5 | 13.68 in. |
| R-60 | 31.5 | 20.50 in. | 108.1 | 16.53 in. |
Spray foam thickness
At the typical R per inch in the DOE Building America, Spray Foam Insulation guide.
| Foam | R per inch | R-13 | R-19 | R-30 |
|---|---|---|---|---|
| Open-cell | 3.6 | 3.6 in. | 5.3 in. | 8.3 in. |
| Closed-cell | 6.0 | 2.2 in. | 3.2 in. | 5.0 in. |
Insulation questions
How much insulation do I need in my attic?
It depends on your climate zone and what's there now. ENERGY STAR suggests adding R-30 to an uninsulated attic in Zone 1 and R-60 in the colder zones, or R-25 to R-49 if you already have 3–4 in. Pick your zone above and the calculator starts from its figure. Zones follow the IECC climate zone map; your local building department can tell you yours.
How many bags of blown-in insulation do I need?
Read it off the chart on the bag: each R-value lists a minimum number of bags per 1,000 sq ft and a minimum depth, and you need both. For 1,000 sq ft at R-49, that's 25 bags of Owens Corning AttiCat PINK, 27.5 lb bag, or 84 bags of Greenfiber INS541LD, 19.05 lb bag. Cellulose is denser and comes in smaller bags, so it takes more of them.
How thick should attic insulation be?
For blown fiberglass, the Owens Corning AttiCat PINK, 27.5 lb bag chart lists at least 17.00 in. for R-49 and 20.50 in. for R-60. Cellulose is denser: about 13.68 in. settled for R-49. Put rulers or depth markers on the joists before you blow so you can check the depth across the whole attic.
How much spray foam do I need?
Spray foam is sold in board feet: 1 sq ft, 1 in. thick. Divide the R-value you want by the foam's R per inch for the thickness, then multiply by the area. For example, R-19 under a 1,000 sq ft floor takes about 3.2 in. of closed-cell foam, or 3,167 board feet. Kits list their board feet on the box; enter it above to count kits.
What R-value do I need for walls?
Batts are made to fit the framing depth, so the wall's studs decide most of it; the batt's R-value is printed on the bag. When siding comes off an uninsulated wall, ENERGY STAR suggests blowing insulation into the empty cavities and adding insulating sheathing in colder zones. Enter the wall area (length × height) with Batts selected to count bags.
How much does insulation cost?
Enter the price per bag (or per spray foam kit) and the calculator multiplies it by the count. Hired installation, air sealing and spray foam by a contractor vary widely by region, so get quotes and use these quantities to compare them.