Building envelope · Units
U-value converter: metric and imperial
Multiply a U-value in W/m²K by 0.1761 to get Btu/h·ft²·°F, and an R-value in m²K/W by 5.678 to get the US R-value. A window of U 1.4 W/m²K is U-0.247 in US units, R 0.714 m²K/W or R-4.06.
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U, W/m²K
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U, Btu/h·ft²·°F
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R, m²K/W
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R (US)
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How it is worked out
U (Btu/h·ft²·°F) = U (W/m²K) × 0.1761102
U (W/m²K) = U (Btu/h·ft²·°F) × 5.678263
R = 1 / U in each system
R (US, h·ft²·°F/Btu) = R (m²K/W) × 5.678263
The factor comes from 1 Btu/h = 0.29307 W, 1 ft² = 0.092903 m² and a temperature step of 1 °F = 5/9 K: 0.29307 / (0.092903 × 5/9) = 5.678. For the window above: 1.4 × 0.1761 = 0.247; its R is 1 / 1.4 = 0.714 m²K/W, and × 5.678 = R-4.06.
What this page does not do
- It does not work out a U-value. For a wall or roof from its layers, or a window from its glass and frame, use the calculators below.
- It does not mix up U and R. U is how much heat passes (lower is better); R is how well it resists (higher is better).
Questions people ask
- How do I convert a U-value from W/m²K to imperial?
- Multiply by 0.1761: U 1.4 W/m²K is U-0.247 Btu/h·ft²·°F.
- How do I convert an R-value from metric to US?
- Multiply the R-value in m²K/W by 5.678: R 2 m²K/W is R-11.4.
- What is the difference between U-value and R-value?
- R = 1 / U. U is the heat that passes per square metre and degree (lower is better); R is the resistance (higher is better).