Insulation Calculator
To estimate insulation, multiply the length × width of the surface for the square footage, then multiply by the installed cost per square foot for your insulation type. Fiberglass batts run about $1–$2.40/ft², blown-in $1–$2.50, and spray foam $3–$7. A 600 ft² area in batts costs roughly $600–$1,440.
- Attic R-value
- R-38 to R-60
- Wall R-value
- R-13 to R-21
- Cheapest type
- Fiberglass batt
Your measurements
Enter your measurements
Fill in the fields to see your estimate.
The formula
Cost = Length × Width × installed price per ft² (by insulation type)How to calculate it manually
- 1
Measure the surface
Multiply length × width for walls, or the attic floor area.
- 2
Pick an insulation type
Batts are cheapest; spray foam gives the highest R-value per inch and air-seals.
- 3
Check the R-value target
Aim for R-38 to R-60 in attics and R-13 to R-21 in walls, depending on climate.
- 4
Estimate cost
Multiply the area by the installed price per square foot for your type.
Example calculation
A 30 ft × 20 ft attic = 600 ft². With fiberglass batts at ~$1.50/ft², that's about $900 installed.
Insulation cost by type
Installed cost per square foot, including materials and labor.
| Type | Cost per ft² (installed) | R-value per inch | Best for |
|---|---|---|---|
| Fiberglass batt | $1.00 – $2.40 | R-3.1 | Walls, budget jobs |
| Blown-in cellulose | $1.00 – $2.50 | R-3.5 | Attics, retrofits |
| Closed-cell spray foam | $3.00 – $7.00 | R-6.5 | Air-sealing, rim joists |
Common insulation estimating mistakes
Under-insulating the attic
The attic is where most heat is lost. Hitting R-38 to R-60 there gives the biggest energy savings.
Ignoring air sealing
Insulation slows heat flow but doesn't stop air leaks. Seal gaps and penetrations first for full performance.
Compressing batts
Squeezing batts into tight cavities lowers their R-value. Use the right thickness for the cavity.
Skipping the vapor barrier
In cold climates, a vapor barrier on the warm side prevents condensation inside walls.
Frequently asked questions
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Ready to start your insulation project?
Run the numbers above, then explore related tools and guides to plan every step.