Insulation R-value
R-value (US) to RSI (metric R-value)
R (ft²·°F·h/BTU) → RSI (m²·K/W)
13 R (ft²·°F·h/BTU) = 2.29 RSI (m²·K/W)
RSI (metric R-value) to R-value (US)
RSI (m²·K/W) → R (ft²·°F·h/BTU)
3.5 RSI (m²·K/W) = 19.87 R (ft²·°F·h/BTU)
R-value (US) to U-factor (BTU/h·ft²·°F)
R (ft²·°F·h/BTU) → BTU/(h·ft²·°F)
19 R (ft²·°F·h/BTU) = 0.05 BTU/(h·ft²·°F)
U-factor (BTU/h·ft²·°F) to R-value (US)
BTU/(h·ft²·°F) → R (ft²·°F·h/BTU)
0.3 BTU/(h·ft²·°F) = 3.33 R (ft²·°F·h/BTU)
U-factor
U-factor (BTU/h·ft²·°F) to U-factor (W/m²·K)
BTU/(h·ft²·°F) → W/(m²·K)
0.3 BTU/(h·ft²·°F) = 1.7 W/(m²·K)
U-factor (W/m²·K) to U-factor (BTU/h·ft²·°F)
W/(m²·K) → BTU/(h·ft²·°F)
1.4 W/(m²·K) = 0.25 BTU/(h·ft²·°F)
Kilocalories per hour-square meter-degree Celsius to U-factor (W/m²·K)
kcal/(h·m²·°C) → W/(m²·K)
1 kcal/(h·m²·°C) = 1.16 W/(m²·K)
U-factor & R-value units at a glance
| Unit | Symbol | In watts per square meter-kelvin | Defined as |
|---|---|---|---|
| Watt per square meter-kelvin | W/(m²·K) | 1 | SI (U) |
| BTU per hour-square foot-degree Fahrenheit | BTU/(h·ft²·°F) | 5.678263 | 5.67826 W/(m²·K) |
| Kilocalorie per hour-square meter-degree Celsius | kcal/(h·m²·°C) | 1.162222 | 1.16222 W/(m²·K) |
| R-value (US) | R (ft²·°F·h/BTU) | — | R-value = 1 ÷ U |
| RSI | RSI (m²·K/W) | — | RSI = 1 ÷ U |
R-value and U-factor are upside down from each other: R = 1 ÷ U. US R-13 wall insulation is RSI 2.29; a window with U-0.30 (US) is 1.70 W/(m²·K).