R-Value to U-Value Converter
Translate insulation thermal resistance (R-value) into thermal transmittance (U-value) instantly. Use the result to verify code compliance, compare wall assemblies, or feed energy model inputs that require U-values.
Use this tool as a quick conversion aid. Always confirm insulation performance with manufacturer data, energy modelling, or code officials.
Examples
- R-13 fiberglass batt ⇒ U ≈ 0.077 W/(m²·K).
- R-21 high-density cavity insulation ⇒ U ≈ 0.048 W/(m²·K).
- R-30 attic assembly ⇒ U ≈ 0.033 W/(m²·K).
FAQ
What happens if I enter R = 0?
The calculator flags invalid entries because dividing by zero is undefined. Verify that you are using the total assembly R-value, not just a single material layer.
Is the output in SI or imperial units?
U-values are shown in W/(m²·K), the SI standard. Multiply by 0.176 to convert to BTU/(hr·ft²·°F) if needed.
Do I need to account for thermal bridges separately?
Yes. If studs or fasteners reduce effective R-value, adjust your input to the assembly's overall R before converting.
Additional Information
- Formula: U-value = 1 ÷ R-value. Higher R reduces heat flow; lower U indicates better insulation performance.
- Most US building codes specify maximum U-values for assemblies. Convert your design R-value to confirm compliance quickly.
- If you work in SI, convert RSI to imperial R by multiplying by 5.678, run the calculation, then multiply the resulting U-value by 5.678 to return to W/(m²·K).
- Real-world performance depends on installation quality, thermal bridging, and air sealing—factors not captured by nominal R-values.