Insulation Calculator
Calculate insulation batts or rolls needed for walls and attics.
Insulation Calculator
What This Calculator Does
The Insulation Calculator tells you how many bags or rolls of insulation you need based on wall or attic area and the target R-value. Enter the surface area and select the R-value to get the number of insulation packages required, plus the coverage per package.
Proper insulation is the single most cost-effective energy efficiency upgrade for US homes. The Department of Energy recommends attic insulation of R-38 to R-60 (depending on climate zone), wall insulation of R-13 to R-21, and floor insulation of R-11 to R-19.
Federal tax credits (up to $1,200/year under the Inflation Reduction Act) are available for qualifying insulation upgrades through 2032 - check ENERGY STAR for current requirements.
How to Use
- Measure the total wall or attic floor area in square feet to be insulated.
- Select the R-value that matches your wall cavity depth and climate zone.
- Enter the area and select R-value in the calculator above.
- Click "Calculate" to see the number of bags/rolls needed.
- Check ENERGY STAR for federal tax credit eligibility on your insulation upgrade.
Worked Examples
Attic Insulation Upgrade
A 1,200 sq ft attic in Climate Zone 4 (mixed) upgrading from R-19 to R-49 using blown-in fiberglass insulation.
- →Existing R-19 at 6 inches depth. Target R-49 at approximately 14.5 inches depth.
- →Additional R-value needed: R-49 - R-19 = R-30.
- →Coverage per bag at R-30: approximately 22 sq ft per bag.
- →Bags needed: 1,200 / 22 = 55 bags.
- →With 10% waste for irregular edges: 55 x 1.10 = 61 bags.
- →At $35 per bag: 61 x $35 = $2,135 material cost. After 30% tax credit: $2,135 x 0.70 = $1,495 net cost.
Result: Approximately 61 bags of blown-in fiberglass needed for an R-49 attic upgrade in a 1,200 sq ft home, costing about $1,500 after federal tax credit.
Before adding insulation, air-seal all attic penetrations (wiring holes, duct gaps, recessed light fixtures) with caulk or spray foam. Air leakage reduces insulation effectiveness by up to 30% — sealing is often more cost-effective than adding more insulation.
Reference Table
| R-Value | Wall Type | Thickness | Coverage per Bag | Common Use |
|---|---|---|---|---|
| R-13 | 2x4 wall | 3.5 in | ~40 sq ft | Exterior walls, South |
| R-15 | 2x4 wall | 3.5 in | ~35 sq ft | Exterior walls, mixed |
| R-19 | 2x6 wall | 5.5 in | ~32 sq ft | Exterior walls, North |
| R-21 | 2x6 wall | 5.5 in | ~28 sq ft | Exterior walls, cold |
| R-30 | Attic floor | 8.5 in | ~22 sq ft | Attic, South |
| R-38 | Attic floor | 11 in | ~16 sq ft | Attic, mixed |
| R-49 | Attic floor | 14.5 in | ~12 sq ft | Attic, cold |
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