Insulation Calculator
Calculate insulation material and cost for fiberglass batt, blown-in, or spray foam by R-value target.
By Konstantin Iakovlev · Updated September 2026 · Source: ENERGY STAR — Recommended Home Insulation R-Values
Total Project Cost
$420.00
Est. Annual Savings
$166.25
Payback Period
2.5 years
Project Details
| Total Area | 400 sq ft |
| Fiberglass Batt (R-19) | 10 rolls |
| Cost per sq ft | $0.55 |
| Material Cost | $220.00 |
| Labor Estimate | $200.00 |
| Total Project Cost | $420.00 |
Energy Savings Estimate
| Heating (gas furnace) | $133.98 |
| Cooling (central air) | $32.27 |
| Estimated Annual Energy Savings | $166.25 |
| Payback Period | 2.5 years |
| 5-Year Net Savings | $411.23 |
| 10-Year Net Savings | $1,242.46 |
Use the Insulation Calculator above to calculate your results. Enter your values and see instant results — all calculations run in your browser.
Disclaimer: This calculator is for informational purposes only. Results are estimates from the numbers you enter and the assumptions described on this page; check them against local building codes, product specifications and current prices, and have structural, electrical or gas work designed or checked by a licensed professional.
How It Works
Estimating how much fiberglass batt, blown-in cellulose, or spray foam you need to hit a target R-value comes down to a few measurable inputs. Tightening up a home's thermal envelope is one of the more reliable ways to cut bills: EPA's ENERGY STAR program estimates that air sealing and adding insulation in attics, floors over crawl spaces and accessible basement rim joists saves an average of 15% on heating and cooling costs, or 11% of total energy costs.
The calculator multiplies the area (length × height or width) by a material price per square foot set by the insulation type and the R-value you pick: fiberglass batts run from $0.40 at R-13 to $0.90 at R-38, blown-in from $1.00 to $2.20 and spray foam from $1.80 to $4.00. Labor is added at a flat $0.50, $0.80 or $1.50 per square foot for the three types. The unit count divides the area by a fixed coverage of 40 sq ft per roll of batts, 25 sq ft per bag of blown-in and 200 sq ft per spray-foam kit, whatever R-value you choose, so check the coverage chart on the product you buy. The R-value options stop at R-38, while ENERGY STAR recommends R49 to R60 for an uninsulated attic in climate zones 2-8.
Annual savings follow the heat that stops flowing through the area: square feet × (1/R before − 1/R after) × degree-days × 24 hours. Heating is priced for a 90%-efficient gas furnace at $1.48 a therm (EIA's 2025 residential average) and cooling for a SEER 14 air conditioner at 18.34¢ per kWh (EIA, June 2026), using rounded degree-days of 1,800 heating and 2,400 cooling for zones 1-3, 4,300 and 1,300 for zone 4, and 6,800 and 600 for zones 5-8. What is already there matters most: the default 400 sq ft of R-19 batts over an empty cavity (about R-4) in zone 4 saves about $166 a year and pays back its $420 cost in 2.5 years, while the same job over 3-4 inches of old fiberglass (about R-11) saves $32 a year and takes 13 years. The degree-day method ignores sunshine and the heat from people and appliances, so real heating savings usually run somewhat lower. The total includes $200 of labor, so doing the work yourself leaves the $220 material cost.
Example: Insulating a 1,500 sq ft Attic with Blown-In
- 1 Input: Area Length 50 ft × Area Height / Width 30 ft = 1,500 sq ft, Insulation Type = Blown-In, R-Value Target = R-38 (the highest option), Existing Insulation = None (about R-4), Climate = Mixed (zone 4).
- 2 Material: 1,500 sq ft × $2.20 per sq ft (blown-in at R-38) = $3,300. Units: 1,500 ÷ 25 sq ft per bag = 60 bags.
- 3 Labor: 1,500 sq ft × $0.80 = $1,200. Total project cost: $3,300 + $1,200 = $4,500.
- 4 Savings: 1,500 × (1/4 − 1/38) = 335.5 Btu per hour per °F. Heating: 335.5 × 4,300 degree-days × 24 ÷ 0.9 = 384.7 therms × $1.48 = $569. Cooling: 335.5 × 1,300 × 24 ÷ 14,000 = 747.7 kWh × $0.1834 = $137. Total about $707 a year, so the $4,500 pays back in 6.4 years; over an existing R-11 layer the same job saves $204 a year and takes 22 years.
- 5 Context: ENERGY STAR recommends R49 for an uninsulated attic in zones 2-3 and R60 in zones 4-8, so across most of the country R-38 falls short. At R-38 the insulation has to be about 38 ÷ 13 = 2.9 times as deep as at R-13, yet the calculator counts the same 25 sq ft per bag at every R-value, so size the order from the coverage chart on the bag.
Source: ENERGY STAR — Recommended Home Insulation R-Values · Last updated: September 2026
Frequently Asked Questions
What R-value insulation do I need?
What type of insulation is the most cost-effective?
How much money does insulation save on energy bills?
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