Insulation Calculator – How Much Do I Need? (R-Value) | CalcLoft
Find out exactly how much insulation you need by area and R-value.
How much insulation do I need?
Insulation is sold by coverage per package (batts or rolls). First find your area, then match the R-value to your location. For a 30 × 30 attic (900 sq ft) at R-38, you need roughly 900 sq ft of R-38 insulation — about 9-12 rolls depending on brand.
Recommended R-values by region (US)
| Zone | Attic | Walls |
|---|---|---|
| Zone 1-2 (South) | R-30 to R-49 | R-13 to R-15 |
| Zone 3-4 (Mid) | R-38 to R-60 | R-15 to R-21 |
| Zone 5-8 (North) | R-49 to R-60 | R-21+ |
Coverage by package type
- Batts (faced): R-13 ≈ 10 sq ft/batt · R-19 ≈ 14 sq ft/batt (varies by brand — check the label)
- Rolls: usually 40-80 sq ft per roll
- Blown-in: sold by the bag (covers ~25-35 sq ft at R-38 depth)
Insulation calculator FAQ
How much insulation for a 1000 sq ft attic?
At R-38: about 1,000 sq ft of insulation — roughly 12-15 rolls or 40 bags of blown-in.
Can I add insulation over old insulation?
Yes for attics — but never cover recessed "IC"-rated lights wrong; check fixtures and keep clearance.
What R-value do I need for walls?
2×4 walls: R-13 to R-15. 2×6 walls: R-19 to R-21. Check your local code.
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