Attic Insulation Calculator
Estimate how much insulation material you need for your attic based on square footage, insulation type, and your target R-value. Use this alongside our cost calculators to plan your full project budget.
R-Value by Insulation Type
| Type | R-Value per Inch | Depth for R-38 | Depth for R-60 |
|---|---|---|---|
| Blown-In Fiberglass | R-2.2–2.7/in | ~15–17 in | ~22–27 in |
| Blown-In Cellulose | R-3.2–3.8/in | ~10–12 in | ~16–19 in |
| Spray Foam (open-cell) | R-3.5–3.6/in | ~11 in | ~17 in |
| Spray Foam (closed-cell) | R-6.0–7.0/in | ~6 in | ~9 in |
| Fiberglass Batts | R-3.1–3.4/in | ~11–12 in | ~18 in |
| Mineral Wool Batts | R-3.0–3.3/in | ~12 in | ~18–20 in |
DOE Recommended R-Values by Climate Zone
How to Calculate Insulation Quantity
- 1
1. Measure attic square footage
Length × width of the attic floor area. Include all accessible areas.
- 2
2. Determine current R-value
Measure existing insulation depth and multiply by the R-value per inch for that material.
- 3
3. Find your target R-value
Use the DOE climate zone table above. Most US homes should target R-38 to R-60.
- 4
4. Calculate additional depth needed
Subtract current R-value from target, then divide by the R-value per inch of your new material.
- 5
5. Estimate bags or rolls needed
Blown-in bags typically cover 40–45 sq ft at recommended depth. Check the bag's coverage chart.