Insulation R-Value Calculator
The Department of Energy publishes recommended R-values by climate zone (Zones 1–8, mapped by state and county) for attics, walls, floors, and basement walls. Higher R-values reduce heat transfer through the building envelope — each R-value point matters more in extreme climates. This calculator looks up the DOE recommendation for your zone and surface, then estimates batt/roll count for walls and floors or blown-in bag count for attics. Attics with R-38 or less should be upgraded to R-49 or R-60 in Zones 5–8 — this is typically the highest ROI insulation improvement in an existing home. Wall cavity insulation is limited by framing depth (R-13/R-15 in 2×4 walls, R-19/R-21 in 2×6 walls), but exterior rigid foam can add R-5 to R-10 to any wall without changing the framing.
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Top PickR-13 Kraft Faced Batts — Home Depotfrom $16.98/bag* Affiliate links — we may earn a commission at no cost to you.
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
What R-value do I need in my attic?
The DOE recommends R-38 to R-60 for attics in most of the US. In warmer climates (Zone 1–3), R-30 to R-38 is sufficient. In cold climates (Zones 5–8), aim for R-49 to R-60. More insulation always reduces energy bills.
What is the R-value of a 2×4 wall?
A 2×4 wall cavity (3.5" deep) holds R-13 or R-15 batts. Adding 1" rigid foam sheathing outside adds another R-5 to R-6, for a total assembly R-value of about R-18 to R-21.
What is my DOE climate zone?
Climate zones run from 1 (hottest — South Florida, Hawaii) to 8 (coldest — Alaska). Zone 2: South Texas, Gulf Coast. Zone 3: Southeast, California coast. Zone 4: Virginia, Kansas, Pacific Northwest. Zone 5: Pennsylvania, Ohio, Colorado. Zone 6: Minnesota, Wisconsin, upstate NY. Zone 7: northern Minnesota, Montana. Look up your county at the DOE's climate zone map for precision.
Is blown-in or batt insulation better for an attic?
Blown-in insulation (fiberglass or cellulose) is better for most attics — it fills irregular cavities around trusses and existing wiring without cutting and fitting individual batts. It also settles into every gap, providing fewer thermal bridges. Batts are appropriate for attic floor cavities when access is good and the layout is regular, but they require careful installation to avoid gaps that defeat their rated R-value.