Attic Insulation Calculator
Enter your climate zone, attic area, existing R-value, and material to calculate the depth and quantity of insulation needed to meet DOE recommendations.
Attic Details
R-value recommendations from ENERGY STAR / U.S. DOE, as of June 2026. Bag count is a planning estimate — verify against the coverage chart on your specific product.
Formula
additional_R = max(0, recommended_R − existing_R)
depth_in = additional_R ÷ R_per_inch
volume_cuft = (area_sqft × depth_in) ÷ 12
bags = ⌈volume_cuft ÷ cuft_per_bag⌉
Cellulose: R-3.7/in settled, 0.82 cu ft/bag (25 lb). Fiberglass blown: R-2.5/in, 1.5 cu ft/bag (30 lb). Batt: R-3.14/in (no bag count).
Related Calculators
- Insulation Calculator — full multi-material tool
- Blown-In Insulation Calculator
- R-Value Calculator
- Spray Foam Calculator
- DOE Climate Zone Reference
Frequently Asked Questions
The U.S. DOE recommends R-30 to R-60 depending on your climate zone. Zone 1 (hottest) requires R-30; Zones 6–8 (coldest) require R-60. Most mid-country homes in Zones 4–5 should target R-49. These are recommendations for existing homes verified from energystar.gov as of June 2026.
Measure the length and width of your home's footprint at the exterior walls — your attic floor area is roughly equal to your home's total conditioned floor area. For irregular shapes, break the space into rectangles and add them together.
Blown-in (loose-fill) insulation fills gaps and irregular spaces better and is ideal for adding insulation on top of existing material. Batts work well in unobstructed joist bays. For most attic upgrades, blown-in cellulose or fiberglass provides better coverage with less labor.
Adding blown-in insulation with a rental blower machine is a common DIY project for unfinished attics with accessible floor joists. Always air-seal first (around can lights, plumbing penetrations, and the attic hatch) before adding insulation. For safety reasons, always verify with your local building department and consult a qualified contractor for complex attics.
The calculator uses the DOE-recommended R-value for your climate zone, subtracts your existing R-value to find the additional insulation needed, then divides by the material's R-value per inch to determine the required depth. For blown-in materials, it converts depth to volume (cubic feet) and divides by the settled coverage per bag.