Insulation R-Value Calculator

Summary

The Insulation R-Value Calculator computes total thermal resistance for one or more insulation layers. Enter the material type and thickness for each layer — or supply a custom R-per-inch value — and the tool sums the R-values and derives the U-factor (1/R-total). Use it to verify code compliance, compare insulation assemblies, or size upgrades before purchasing materials.

How it works

1. Select an insulation material from the dropdown or choose "Custom" to enter your own R-per-inch value.
2. Enter the thickness in inches for that layer.
3. Add more layers with the "Add Layer" button to model a stacked assembly.
4. The calculator multiplies R-per-inch × thickness for each layer, then sums them.
5. Total R-value and U-factor (1 ÷ R-total) update instantly as you type.
6. 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