Insulation Calculator

Enter a target R value or U value and see the thickness needed in common materials plus the heat loss per square metre.

Insulation calculator

What are you targeting?

Target value

Design temperature difference (degC)

Target R value: —

Target U value: —

Heat loss per square metre: —

—

The R value is the thickness divided by the thermal conductivity, and the U value is one divided by the total R value.

Choose whether you are targeting an R value or a U value.
Enter the target value and the design temperature difference.
Compare the thickness needed in each material and the heat loss per square metre.

Common questions about the free online insulation calculator.

R value is the thickness of the material in metres divided by its thermal conductivity, so a thicker or lower conductivity layer gives a higher R.

U value is one divided by the R value. An R value of 3.5 gives a U value of about 0.286 watts per square metre kelvin.

Multiply the target R value by the thermal conductivity of the material. Mineral wool at 0.040 needs 140 mm to reach an R value of 3.5.

It depends on the climate and the building code. Roofs in cold regions often aim for R values of 6 or more, while walls sit between 2.5 and 4.

The lowest conductivity wins, so aerogel at about 0.015 delivers the same R value in roughly a third of the thickness of mineral wool.

It is the rate at which heat passes through a material, measured in watts per metre kelvin. Lower values insulate better.

It does not change the R or the U value, but a larger temperature difference increases the heat loss in watts for every square metre.

The tool works in metric units, with R in square metre kelvin per watt and U in watts per square metre kelvin.

No. The insulation figures are calculated in your browser, so the values you enter are never sent to a server.

Yes. It is completely free, needs no sign-up, and you can compare as many materials and targets as you wish.

Last updated: October 10, 2026