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Insulation R-value calculator

Add the thermal-resistance values shown for each material layer. The tool totals layers in series, accounts for repeated layers and converts R-value to RSI.

Layer 1 name (optional)
Layer 2 name (optional)
Layer 3 name (optional)
Layer 4 name (optional)

This is arithmetic for user-entered layer values in series. It does not estimate whole-wall performance, thermal bridges, air leakage, moisture, material properties, installation quality or code compliance. R and RSI depend on tested product data and assembly conditions. Use manufacturer documentation and local building requirements; consult a qualified professional for design. All calculations run locally in this browser.

How do you calculate total insulation R-value?

For layers in series, multiply each layer value by its quantity and add the contributions. This calculator converts between US R-value and metric RSI and shows the reciprocal U-factor for reference.

Frequently asked questions

How do you calculate total insulation R-value?

For layers in series, multiply each layer value by its quantity and add the contributions. This calculator converts between US R-value and metric RSI and shows the reciprocal U-factor for reference.

Are my insulation values uploaded?

No. The calculation runs locally in your browser; entered layer names and values are not sent to a server or saved by this tool.

Can I add R-values for layers in a wall?

This calculator adds the values you provide as layers in series. It does not account for parallel paths such as studs, gaps or thermal bridges, so the sum is not necessarily the whole-wall effective R-value.

What is the difference between R-value and RSI?

They both describe thermal resistance in different unit systems. This tool uses RSI = R × 0.1761 (approximately) and reports the reciprocal U-factor only as a unit conversion.