R-value measures thermal resistance — how strongly a material resists heat flow. Higher R-value means better insulation. Values are additive: two layers with R-13 and R-5 give a combined R-18.

U-factor (thermal transmittance) is the inverse of total R-value: U = 1 ÷ R. It measures heat flow rate per square foot per degree of temperature difference. Lower U-factor means better thermal performance.

Are R-values per inch accurate for all densities?

Preset values use industry-standard nominal figures. Actual performance varies slightly by product density, moisture content, and age. Always confirm with manufacturer data for code submissions.

Does this include air films or framing factors?

No. This tool covers only the insulation layers you add. For a full assembly R-value (including interior/exterior air films, sheathing, and framing), add each component as a separate custom layer.

What R-value do I need for my climate zone?

IECC 2021 requirements range from R-13 walls (zone 1) to R-49 attics (zones 6–8). Check your local building code or the DOE's climate zone map for the required values in your area.

Insulation R-Value Calculator

Name: Insulation R-Value Calculator
Availability: InStock
Author: Nham Vu

Calculate total R-value and U-factor for single or stacked insulation layers using preset material values or custom entries.

Insulation Layers

R-per-inch values are nominal industry figures. Add layers for a stacked assembly.

Results

Total R-Value

—

h·ft²·°F/BTU

U-Factor (1 ÷ R)

—

BTU/h·ft²·°F

Add at least one layer on the left to see results.

Common R-Values per Inch

Material	R / inch

Summary

Calculate total R-value and U-factor for single or stacked insulation layers using preset material values or custom entries.

How it works

Select an insulation material from the dropdown or choose "Custom" to enter your own R-per-inch value.
Enter the thickness in inches for that layer.
Add more layers with the "Add Layer" button to model a stacked assembly.
The calculator multiplies R-per-inch × thickness for each layer, then sums them.
Total R-value and U-factor (1 ÷ R-total) update instantly as you type.
Remove any layer with the × button to revise your assembly.

Use cases

Check whether a wall or attic assembly meets local energy code R-value requirements.
Compare fiberglass batt vs. spray foam to decide which meets a target R-value in less space.
Model an existing assembly (drywall + batt + sheathing) to find the current baseline before adding insulation.
Calculate U-factor for Manual J / HVAC load calculations.
Quickly verify contractor quotes list enough material to reach the specified R-value.
Size insulation upgrades for a retrofit project on a fixed budget.

Frequently Asked Questions

Last updated: 2026-06-11 · Reviewed by Nham Vu