How Much Insulation Do I Need?
Two separate questions decide this: what R-value your climate needs (look up your zone below), and how many bags of your chosen product cover your area (divide your square footage by the coverage printed on the bag). The insulation calculator handles the second part — including door and window subtraction for walls — once you know your target R-value and product. This page is the climate-zone table itself, plus a worked comparison of how much bag count changes between a low- and high-R-value product on the same area.
Recommended attic R-value by climate zone
| IECC climate zone | Region | Recommended attic R-value |
|---|---|---|
| 1–2 | Warmest (Gulf Coast, southern Florida, Hawaii) | R-30 to R-49 |
| 3–5 | Moderate (most of the continental US) | R-38 to R-60 |
| 6–8 | Coldest (northern states, Alaska) | R-49 to R-60 |
US DOE / Energy Star, Recommended Home Insulation R-Values publishes this table by IECC climate zone; wall cavities are typically R-13 to R-21 depending on stud depth, a separate figure from the attic table above. Once you know your target R-value, the number of bags you need depends entirely on your chosen product's coverage per bag — not on R-value directly, which is what the worked example below shows.
A full example: why R-value changes the bag count so much
Take the same 800 sq ft attic floor, insulated two different ways. With a low-R-value product like an R-13 batt — thin enough to cover roughly 100 sq ft per bag — that's 800 ÷ 100 = 8 bags. With a high-R-value product like an R-38 batt — thick enough to cover as little as 30–40 sq ft per bag — the same 800 sq ft needs 800 ÷ 35 ≈ 22.9, rounded up to 23 bags. The area didn't change; the product did, and coverage per bag is what actually drives the count. This is why the calculator's default coverage figure (64 sq ft per bag, a representative mid-range wall batt) is deliberately editable rather than fixed — jumping from a wall-grade to an attic-grade product without updating that number would understate a real order by nearly 3x.