How much insulation do I need?
Pick your climate zone and where you are insulating, then type the area and the R-value per inch of your insulation. The insulation calculator gives the recommended R-value to add, the depth, and how much insulation fills the space.
- R-value to add
- 60
Add R-60: about 20 inches of insulation, 1,667 cubic feet over the area.
- Depth (in)
- 20
- Depth (cm)
- 50.8
- Volume (ft³)
- 1,667
- Volume (m³)
- 47.19
- RSI to add
- 10.57
R-value to add: 60. Add R-60: about 20 inches of insulation, 1,667 cubic feet over the area.
How to calculate
Finds the R-value to add to an attic or floor for your climate zone, the depth of insulation that gives it, and the volume to cover the area.
Example with the default inputs (Climate zone Zone 4A or 4B, Where Attic, none yet, Area to insulate 1,000 ft², R-value per inch 3): Add R-60: about 20 inches of insulation, 1,667 cubic feet over the area.
Method: R to add = the zone’s value for the place; depth (in) = R ÷ R per inch; volume = area × depth.
- The R-values are ENERGY STAR’s recommendations for adding insulation to existing wood-framed homes; your local code may ask for more in new work.
- R-value per inch differs by product and how it is installed; use the number on the bag or batt label when you have it.
- Blown insulation settles; the bag label gives the installed depth and the number of bags for each R-value, which this page does not count.
Worked examples
Each example is checked against the calculator on every build.
- Climate zone Zone 4A or 4B, Where Attic, none yet, Area to insulate 1,000 ft², R-value per inch 3 gives R-value to add 60, Depth (in) 20, Depth (cm) 50.8, Volume (ft³) 1,666.666667, RSI to add 10.566612.Source: ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zone 4A and 4B, uninsulated attic: R60); ENERGY STAR, How to Check Your Home’s Attic Insulation Level (fiberglass, cellulose and mineral wool about R-3 to R-3.5 per inch; depth × 3), https://www.energystar.gov/products/ask-the-experts/how-check-your-homes-attic-insulation-level
- Climate zone Zone 2, Where Attic, 3–4 in already, Area to insulate 1,500 ft², R-value per inch 2.5 gives R-value to add 38, Depth (in) 15.2, Volume (ft³) 1,900.Source: ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zone 2, 3–4 in existing: add R38)
- Climate zone Zone 7 or 8, Where Floor, Area to insulate 1,076 ft², R-value per inch 3.5 gives R-value to add 38, Depth (in) 10.857143, Volume (m³) 27.577143.Source: ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zones 7 and 8, floor: R38)
- Climate zone Zone 1, Where Attic, none yet, Area to insulate 1,000 ft², R-value per inch 3 gives R-value to add 30, Depth (in) 10.Source: ENERGY STAR, Recommended Home Insulation R-Values (retrofit of existing wood-framed buildings, based on 2021 IECC Table R402.1.3), https://www.energystar.gov/saveathome/seal_insulate/identify-problems-you-want-fix/diy-checks-inspections/insulation-r-values (zone 1, uninsulated attic: R30); DOE, Energy Efficient Home Improvement Credit: Insulation and Air Sealing (zone 1 uninsulated attic R30), https://www.energy.gov/cmei/buildings/articles/energy-efficient-home-improvement-credit-insulation-and-air-sealing
How it works
- R-value to add comes from the table for your zone and place (US units, ft²·°F·h/Btu):
| Zone | Attic, none yet | Attic, 3–4 in already | Floor |
|---|---|---|---|
| 1 | R30 | R25 | R13 |
| 2 | R49 | R38 | R13 |
| 3 | R49 | R38 | R19 |
| 4A or 4B | R60 | R49 | R19 |
| 4C, 5 or 6 | R60 | R49 | R30 |
| 7 or 8 | R60 | R49 | R38 |
- Depth in inches = R to add ÷ R-value per inch; in centimetres × 2.54.
- Volume = area × depth, in ft³ and m³ (1 ft² = 0.09290304 m², 1 in = 0.0254 m).
- RSI = R × 0.1761102.
Rules. Area from 0.1 m² to 1,000,000 m²; R-value per inch from 1 to 8.
Exact arithmetic. The area and the R-value per inch are read as the exact decimals you typed, so depth and volume are exact fractions rounded once.
Output format. The R-value is a whole number; depth shows 1 decimal, cubic feet 0 decimals, cubic metres and RSI 2 decimals, each rounded half up.
Assumptions
- The values are ENERGY STAR’s retrofit recommendations for wood-framed homes (the DOE gives the same uninsulated-attic values). New construction follows your local code.
- R-value per inch varies by product; about 3 is typical for blown fiberglass, cellulose and mineral wool. Use the label of the product you buy.
- The page does not count bags: blown insulation settles, so use the coverage chart on the bag for the R-value you want.
Worked examples by hand
Zone 4A, attic with none, 1,000 ft², R-3 per inch. R to add 60. Depth 60 ÷ 3 = 20 in = 50.8 cm. Volume 1,000 × 20 ÷ 12 = 1,667 ft³ (47.19 m³). RSI 60 × 0.1761102 = 10.57.
Zone 2, attic with 3–4 in, 1,500 ft², R-2.5 per inch. R to add 38. Depth 38 ÷ 2.5 = 15.2 in. Volume 1,500 × 15.2 ÷ 12 = 1,900 ft³.
Zone 7, floor, 100 m², R-3.5 per inch. R to add 38. Depth 38 ÷ 3.5 = 10.857 in = 27.58 cm. Volume 100 × 0.27577 = 27.58 m³.
Zone 1, attic with none, R-3 per inch. R to add 30; depth 10 in.
Other questions people ask
How much attic insulation do I need?
It depends on your climate zone. For an attic with no insulation, ENERGY STAR recommends adding R30 in zone 1, R49 in zones 2 and 3, and R60 in zones 4 to 8. With 3 to 4 inches already there, add R25 in zone 1, R38 in zones 2 and 3, and R49 in zones 4 to 8.
How deep should the insulation be?
Divide the R-value by the R-value per inch of your insulation. Fiberglass, cellulose and mineral wool give about R-3 to R-3.5 per inch, so R60 at R-3 per inch is 20 inches deep, and R38 at R-2.5 per inch is 15.2 inches.
How much insulation do I need to buy?
The volume is the area times the depth: 1,000 ft² at 20 inches is 1,000 × 20 ÷ 12 = 1,667 ft³. Each bag of blown insulation lists how many square feet it covers at each R-value; use that chart to count bags.
What climate zone am I in?
The International Energy Conservation Code splits the US into zones 1 (hottest) to 8 (coldest), some with A, B or C parts. The DOE page in the sources has a map and a link to look up your zone.
What R-value does a floor need?
For a floor over an unheated space such as a crawl space or garage, ENERGY STAR recommends R13 in zones 1 and 2, R19 in zones 3 and 4A or 4B, R30 in zones 4C, 5 and 6, and R38 in zones 7 and 8.
What is RSI?
The metric R-value, in m²·K/W. One US R unit is 0.1761102 RSI, so R60 is RSI 10.57.