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Insulation R-Value Calculator

Estimate total nominal R-value from insulation thickness and R-value per inch.

Updated April 13, 2026
Free online tool
Planning and research use

Why this page exists

Insulation planning is easier when thickness and material R-value per inch are turned into one total R-value estimate. This calculator helps visitors estimate total nominal R-value from those two basic inputs.

Interactive tool

Run the estimate

Enter your numbers and read the result first, then use the sections below to understand what affects the outcome.

Calculator

Insulation R-value calculator

Estimate total R-value from insulation thickness and material R-value per inch.

Result

R-20.4

Estimated total nominal R-value from the insulation thickness and R-value per inch entered.

Total R-valueR-20.4

Thickness used5.5 in

R-value per inch used3.70

Formula usedThickness x R-value per inch

5.5 inches at about R-3.70 per inch works out to roughly R-20.4.
The result is a nominal material estimate, which is why whole-wall or whole-roof performance can still land below the simple material R-value shown.
Use the number for quick planning and comparison, then confirm the actual assembly performance with the product specs and the full construction details.

This is a nominal material R-value estimate. Whole-assembly performance can differ because framing, gaps, compression, moisture, and installation quality all affect real thermal performance.

Planning note

Last updated April 13, 2026. Use this tool to compare scenarios and plan ahead, then confirm important details with the lender, employer, insurer, contractor, or other qualified provider involved in the final decision.

How it works

What the calculator is doing

Enter the insulation thickness and the material R-value per inch.

The calculator multiplies those two values together.

It shows the resulting nominal total R-value along with the assumptions used.

Understanding your result

This is a nominal material estimate, not a whole-assembly performance rating. Framing, compression, gaps, moisture, and installation quality can all change real thermal performance.

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Examples

Ways people use this tool

Example scenarios help turn a quick estimate into a more useful comparison or planning step.

Check what one insulation depth implies

A quick R-value estimate can help when you want to compare thickness options before shopping or quoting.

Compare two insulation materials

Changing the R-value per inch shows how different materials can land at different total R-values for the same cavity depth.

Use it with attic tools

R-value checks often fit naturally beside attic-insulation-cost, BTU, and ventilation planning.

FAQ

Common questions

How is total R-value calculated here?

The calculator multiplies insulation thickness by the R-value per inch entered.

Why call the result nominal R-value?

Because real whole-assembly performance can differ from the simple material rating once framing, gaps, compression, and installation conditions are involved.

Can this replace product specifications or code guidance?

No. It is a quick planning estimate, so final choices should still be checked against product specs and local requirements.

Related tools

Keep comparing

Use these related tools to compare nearby scenarios, check a second estimate, or keep narrowing down the right decision.

Home ToolsUpdated April 12, 2026