CONSTRUCTION · ENERGY

Insulation Calculator

Estimate the rolls, bags, or kits of insulation needed for your project. Compare batt, blown-in, and spray foam options across R-values with cost estimates.

LAST REVIEWED · APR 24, 2026 · BY D. MARQUEZ, P.E.
You need
12 rolls
Insulation DetailsReset
AreaTotal coverage area
sq ft
Insulation type
R-valueHigher = better
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How the insulation calculator works

Enter the area to insulate, choose your insulation type, and select the target R-value. The calculator determines how many rolls (batt), bags (blown-in), or kits (spray foam) you need, with a 10% waste factor for cuts around studs, pipes, and electrical boxes.

Recommended R-values by location

  • Attic — R-38 to R-60 (most climate zones)
  • Exterior walls — R-13 to R-21
  • Floors over unconditioned spaces — R-25 to R-30
  • Crawl space walls — R-13 to R-19

Insulation type comparison

Batt insulation is the most DIY-friendly and affordable. Blown-in fills irregular cavities and existing walls better. Spray foam provides the highest R-value per inch and doubles as an air barrier, but costs 2–3x more.

Methodology. Area with waste = Area × 1.10. Units needed = ceil(Area with waste ÷ Coverage per unit). Cost adjusted by R-value multiplier: R-13 (1.0×), R-19 (1.3×), R-30 (1.8×), R-38 (2.2×). Base prices: batt $1.00/sq ft, blown $1.50/sq ft, spray $2.50/sq ft.

Sources

  • DOE recommended R-values by climate zone
  • ENERGY STAR home insulation guidelines
  • Average insulation prices by type (Home Depot, Lowe's, 2026)
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Frequently asked questions

What R-value do I need for my attic? +
In most of the US (climate zones 4–7), the DOE recommends R-49 to R-60 for attics. In warmer southern regions (zones 1–3), R-38 is sufficient. Check the DOE climate zone map for your specific area.
Can I add insulation over existing insulation? +
Yes — adding insulation over existing batts or blown-in is one of the most cost-effective energy upgrades. Just lay new unfaced batts perpendicular to the existing layer. Never compress existing insulation — it reduces its R-value.
Is spray foam worth the cost? +
Spray foam costs 2–3x more than batt but provides superior air sealing, higher R-value per inch (R-6.5/inch for closed-cell vs R-3.7 for fiberglass), and doubles as a moisture barrier. It's most valuable in rim joists, crawl spaces, and cathedral ceilings.
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