R-Value Calculator

Determine the recommended R-value for your home based on your climate zone and the part of the house being insulated. Then calculate the insulation thickness required to achieve that R-value with your chosen insulation material.

Enter Your Measurements

Climate Zone (1-7)

Application (1=Attic, 2=Wall, 3=Floor)

Insulation R-Value per Inch(/in)

Results

Recommended R-Value

Thickness Needed

14.0

inches

Practical Thickness

14.0

inches

Actual R-Value at Thickness

49.0

Formula

Thickness = Recommended R-Value ÷ R per Inch

How to Use This Calculator

How to Use

1
Enter your climate zone (1 = hot/humid, 7 = very cold). Find your zone at energy.gov or from your local building code.
2
Select the application: attic, wall, or floor.
3
Enter the R-value per inch of your chosen insulation (fiberglass batts = 3.2, cellulose = 3.5, closed-cell foam = 6.5).

Frequently Asked Questions

What climate zone am I in?

The US is divided into 7 climate zones. Zone 1 is hot/humid (southern Florida, Hawaii), Zone 4 is moderate (much of the mid-Atlantic), and Zone 7 is very cold (northern Minnesota, Alaska). Check the DOE climate zone map or your local building code.

What R-value do I need in my attic?

Most energy codes recommend R-38 to R-60 for attics depending on your climate zone. Zones 1-3 require R-30 to R-38, while zones 4-7 require R-49 to R-60.

Does more insulation always mean better?

There are diminishing returns with insulation. Going from R-0 to R-19 saves far more energy than R-19 to R-38. Beyond the recommended R-value for your zone, additional insulation provides minimal benefit relative to cost.

In-Depth Guides

📖

Insulation R-Value Guide: What You Need by Climate Zone

Understand insulation R-values for your climate zone. Covers DOE recommendations for attics, walls, and floors, plus R-value per inch for all common insulation types.

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About This Calculator

This calculator uses the formula: Thickness = Recommended R-Value ÷ R per Inch. All calculations follow industry-standard methods. Results are estimates — always verify with a licensed professional for structural or code-compliant work.

Built and maintained by the CalcSmart team. Last updated March 2026.

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