Heat Transfer Coefficient Converter
Convert heat transfer coefficients and U-values between W/(m²·K), kW/(m²·K), BTU/(h·ft²·°F), kcal/(h·m²·°C) and cal/(s·cm²·°C).
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Heat Transfer Coefficient units
Every unit below converts to every other one in the calculator. Values are relative to the base unit, the watt per square meter kelvin (W/(m²·K)).
| Unit | Symbol | System | Value |
|---|---|---|---|
| Watt per square meter kelvin | W/(m²·K) | SI | Base unit |
| Kilowatt per square meter kelvin | kW/(m²·K) | SI | = 1000 W/(m²·K) |
| BTU per hour square foot degree Fahrenheit | BTU/(h·ft²·°F) | US customary | ≈ 5.678263341 W/(m²·K) |
| Kilocalorie (IT) per hour square meter degree Celsius | kcal/(h·m²·°C) | metric | = 1.163 W/(m²·K) |
| Calorie (thermochemical) per second square centimeter degree Celsius | cal/(s·cm²·°C) | CGS | = 41840 W/(m²·K) |
Watt per square meter kelvin quick reference
| Watt per square meter kelvin | BTU per hour square foot degree Fahrenheit |
|---|---|
| 1 W/(m²·K) | ≈ 0.1761101837 BTU/(h·ft²·°F) |
| 10 W/(m²·K) | ≈ 1.761101837 BTU/(h·ft²·°F) |
| 100 W/(m²·K) | ≈ 17.61101837 BTU/(h·ft²·°F) |
| 1000 W/(m²·K) | ≈ 176.1101837 BTU/(h·ft²·°F) |
Among the 5 heat transfer coefficient units on this page, the smallest is the watt per square meter kelvin (W/(m²·K)) and the largest is the calorie (thermochemical) per second square centimeter degree celsius (cal/(s·cm²·°C)).
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About heat transfer coefficient units
A heat transfer coefficient is heat flow per unit area for each degree of temperature difference. Its SI unit is the watt per square meter kelvin, W/(m²·K). The same unit is used for the U-value (overall heat transfer coefficient) of walls, roofs and windows, where lower means better insulated.
One BTU/(h·ft²·°F) is about 5.6783 W/(m²·K), and one kcal/(h·m²·°C) (IT) is exactly 1.163 W/(m²·K). A U-value is the reciprocal of the total R-value: U = 1 ÷ RSI in SI units, and U = 1 ÷ R in US units.
Frequently asked questions
- How do I convert a US U-factor to W/(m²·K)?
- Multiply by about 5.67826. A window with a U-factor of 0.30 BTU/(h·ft²·°F) is about 1.70 W/(m²·K).
- How do I get a U-value from an R-value?
- Take the reciprocal. RSI 2.5 m²·K/W gives 0.4 W/(m²·K), and US R-20 gives 0.05 BTU/(h·ft²·°F).
- How many BTUs per hour square foot degree Fahrenheit are in one watt per square meter kelvin?
- One watt per square meter kelvin ≈ 0.1761101837 BTU/(h·ft²·°F) (BTUs per hour square foot degree Fahrenheit).