Insulation Calculator
Insulation quantity depends on the area to be insulated, the R-value target, and whether you are using batt insulation (rolls) or blown-in loose-fill (bags). This calculator covers the five most common residential insulation scenarios: R-13 fiberglass batts for 2x4 walls, R-19 batts for 2x6 walls, R-30 batts for floors or shallow attics, R-38 blown-in for attics in most US climate zones, and R-49 blown-in for the coldest zones. Enter the total area in square feet and select your insulation type; the calculator divides the area by the typical coverage per roll or bag and rounds up. Coverage per roll and bag varies by manufacturer and product; the figures used here are typical mid-range values. Always check the coverage chart printed on the specific product you purchase. The US Department of Energy recommends R-values by climate zone and provides a zip-code lookup tool at energy.gov. For walls in most US climate zones, R-13 to R-21 is recommended; for attics, R-38 to R-60 depending on zone. Insulation reduces heating and cooling costs significantly and is one of the best return-on-investment home energy improvements available to homeowners.
Insulation R-value guide (US DOE)
| Location | Zone 1-2 (South) | Zone 3-4 (Mid) | Zone 5-8 (North) |
|---|---|---|---|
| Attic | R-30 to R-38 | R-38 to R-49 | R-49 to R-60 |
| Wall (2x4) | R-13 | R-13 to R-15 | R-15 to R-21 |
| Wall (2x6) | R-19 | R-19 to R-21 | R-21 |
| Floor | R-13 | R-19 to R-25 | R-25 to R-30 |
Insulation calculator: frequently asked questions
What R-value do I need for my walls and attic?
The US Department of Energy recommends R-values based on your climate zone. For most of the continental US, attic insulation should be R-38 to R-60 and wall insulation R-13 to R-21. Climate Zone 1 (southern Florida, Hawaii) needs R-30 to R-38 in the attic. Climate Zone 7 (northern Minnesota, Alaska) needs R-49 to R-60. The DOE zip-code-based tool at energy.gov provides the exact recommendation for your location.
How do batts differ from blown-in insulation?
Batt insulation comes in pre-cut rolls or segments that fit between standard framing studs or joists (16 or 24-inch centres). Blown-in (loose-fill) insulation is blown into attic spaces or wall cavities using a machine. Blown-in provides better coverage around obstructions and irregular framing. Fiberglass batts are sold in rolls; blown-in fiberglass and cellulose are sold in bags. This calculator handles both formats.
How much insulation is in a bag?
Bag coverage varies by product and R-value. A typical bag of blown-in fiberglass covers about 40 to 65 square feet at the coverage depth required for each R-value. Each bag has a coverage chart printed on it. For R-38, a standard 40 lb bag of blown fiberglass covers approximately 19 to 25 square feet. For R-49, coverage is approximately 14 to 18 square feet per bag. Always use the chart on the specific product you purchase.
Can I add insulation on top of existing insulation?
Yes. Adding insulation on top of existing attic insulation is one of the most cost-effective energy upgrades you can make. If the existing insulation is in good condition and not compressed, you can simply lay batts perpendicular to the existing ones, or blow in additional loose-fill on top. The US DOE recommends achieving the total R-value for your zone, counting both old and new layers together.
Do I need a vapour barrier with insulation?
In most US climate zones, a vapour retarder is required on the warm-in-winter side of the insulation to prevent moisture from migrating into the wall or attic cavity and causing condensation, mould, and rot. In cold climates (zones 5 through 8), the vapour retarder goes on the interior side. In hot-humid climates (zones 1 through 3), it may go on the exterior side or be omitted in favour of permeable materials. Check your local building code and the IRC requirements for your zone.
Sources
- US DOE Energy Saver, Insulation: energy.gov/energysaver/insulation.
- US DOE climate zone map and R-value recommendations: energy.gov/energysaver/where-insulate-home.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology. Coverage estimates are typical; verify with product packaging.