Heat Transfer Coefficient Converter
Convert heat transfer coefficients between watts per square metre per kelvin, Btu per hour per square foot per degree Fahrenheit, kilocalorie and calorie units, and CHU. Enter a value, choose the units and read the result instantly.
Select two units to see the conversion factor.
The heat transfer coefficient (W/(m²·K)) is not thermal conductivity (W/(m·K)), not thermal resistance (K/W) and not heat flux density (W/m²).
Heat Transfer Coefficient Formula
The heat transfer coefficient h relates heat flux to temperature difference: h = q″ ÷ ΔT = Φ ÷ (A × ΔT), in W/(m²·K). Every unit is a fixed multiple of W/(m²·K). Result = value × (source factor ÷ target factor). Exact building blocks: 1 Btu (IT) = 1,055.05585262 J, 1 ft = 0.3048 m, 1 °F interval = 5/9 K, 1 cal (IT) = 4.1868 J, 1 CHU = 1,899.1005 J. For example 1 Btu(IT)/(h·ft²·°F) ≈ 5.678 W/(m²·K).
What Is the Heat Transfer Coefficient?
The heat transfer coefficient h says how much heat crosses each square metre of a surface or layer for every kelvin of temperature difference across it: q″ = h × ΔT. Still air against a wall has a coefficient of about 5 to 10 W/(m²·K), forced air 10 to 100, and boiling water several thousand. Building codes call the overall version the U-value.
It combines conduction, convection and radiation for a particular surface or assembly. A single material is described by thermal conductivity (W/(m·K)); a layer’s coefficient is its conductivity divided by thickness. Thermal resistance of an object (K/W) and the area-based R-value (m²·K/W, the reciprocal of h) are different quantities and are not converted here. Heat flux density (W/m²) does not include temperature; you multiply the coefficient by a temperature difference to get it.
The temperature in the unit is an interval. A kelvin and a Celsius degree are the same size, while a Fahrenheit degree is 5/9 of that, which is why the Btu/(h·ft²·°F) number is smaller than the SI number by about 5.7. No offsets are applied. Area scales as the square of length: 1 ft² = 0.09290304 m².
Supported Units
This converter supports the following 11 heat transfer coefficient units. The last column gives the value of each unit in the base unit W/(m²·K).
| Unit | Symbol | Value in W/(m²·K) |
|---|---|---|
| Watt per square meter per kelvin | W/(m²·K) | 1 |
| Watt per square meter per °C | W/(m²·°C) | 1 |
| Joule per second per square meter per kelvin | J/(s·m²·K) | 1 |
| Calorie (IT) per second per square centimeter per °C | cal(IT)/(s·cm²·°C) | 41,868 |
| Kilocalorie (IT) per hour per square meter per °C | kcal(IT)/(h·m²·°C) | 1.163 |
| Kilocalorie (IT) per hour per square foot per °C | kcal(IT)/(h·ft²·°C) | 12.51842781 |
| Btu (IT) per second per square foot per °F | Btu(IT)/(s·ft²·°F) | 20,441.74803 |
| Btu (th) per second per square foot per °F | Btu(th)/(s·ft²·°F) | 20,428.07723 |
| Btu (IT) per hour per square foot per °F | Btu(IT)/(h·ft²·°F) | 5.678263341 |
| Btu (th) per hour per square foot per °F | Btu(th)/(h·ft²·°F) | 5.674465897 |
| CHU per hour per square foot per °C | CHU/(h·ft²·°C) | 5.678263341 |
How to Use the Heat Transfer Coefficient Converter
- Type the heat transfer coefficient in the value box. Decimals and scientific notation such as 0.0025 or 2.5e-3 are accepted.
- Choose the From unit and the To unit.
- The result appears instantly, or press Convert Now. Very large or very small results are shown in scientific notation.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this value in all units for a full list, and Clear to start again.
Step-by-step by hand
- Find the size of each unit in the common base unit (W/(m²·K)): 1 Btu(IT)/(h·ft²·°F) = 5.678263341 W/(m²·K) and 1 W/(m²·K) = 1 W/(m²·K).
- Divide the source size by the target size to get the conversion factor: 5.678263341 ÷ 1 = 5.678263341, so 1 Btu(IT)/(h·ft²·°F) = 5.678263341 W/(m²·K).
- Multiply by your value: 0.5 Btu(IT)/(h·ft²·°F) × 5.678263341 = 2.839131671 W/(m²·K).
The coefficient is positive, so only zero and positive values are accepted.
Common Heat Transfer Coefficient Conversions
- Imperial to metric: 0.5 Btu/(h·ft²·°F) equals 2.839131671 W/(m²·K).
- Metric to imperial: 2.8 W/(m²·K) equals 0.4931085143 Btu/(h·ft²·°F).
- Kilocalories: 10 kcal/(h·m²·°C) equals 11.63 W/(m²·K).
- Per second: 0.001 cal/(s·cm²·°C) equals 41.868 W/(m²·K).
- CHU: 1 CHU/(h·ft²·°C) equals 5.678263341 W/(m²·K).
- Heat flow estimate: h = 25 W/(m²·K) with ΔT = 40 K gives q″ = 1,000 W/m².
W/(m²·K) to Btu/(h·ft²·°F)
Quick reference for frequently used values
| W/(m²·K) | Btu(IT)/(h·ft²·°F) | kcal(IT)/(h·m²·°C) | cal(IT)/(s·cm²·°C) |
|---|---|---|---|
| 1 | 0.1761101837 | 0.8598452279 | 2.388458966e-5 |
| 2 | 0.3522203674 | 1.719690456 | 4.776917933e-5 |
| 5 | 0.8805509184 | 4.299226139 | 0.0001194229483 |
| 10 | 1.761101837 | 8.598452279 | 0.0002388458966 |
| 25 | 4.402754592 | 21.4961307 | 0.0005971147416 |
| 100 | 17.61101837 | 85.98452279 | 0.002388458966 |
| 1,000 | 176.1101837 | 859.8452279 | 0.02388458966 |
Where and Why This Conversion Is Used
- Building design: U-values of windows, walls and roofs.
- Heat exchangers: film and overall coefficients.
- HVAC and refrigeration: coil and surface sizing.
- Electronics cooling: convective coefficients of heat sinks.
- Textbooks and handbooks: data in metric, US and calorie-based units.
Limitations
- A coefficient depends on flow, geometry and fluid; this tool changes units only.
- The reciprocal R-value (m²·K/W) and thermal conductivity are separate quantities and are not converted here.
- Make sure ΔT is a temperature difference and not a temperature reading.
Important Differences Between Related Heat Quantities
- Specific heat capacity, J/(kg·K): energy needed to warm one kilogram of a material by one kelvin. It is not the total heat capacity of an object (J/K), which also depends on how much material there is, and it is not molar heat capacity (J/(mol·K)).
- Heat density, J/m²: heat or radiant energy delivered per unit area over a period. Heat flux density, W/m² is the rate of that transfer, energy per area per time. They are not interchangeable.
- Heat flux density, W/m² is heat flow per area. The heat transfer coefficient, W/(m²·K) is heat flux per kelvin of temperature difference, so heat flux = coefficient × temperature difference.
- Thermal conductivity, W/(m·K) is a material property. The heat transfer coefficient is a property of a surface or an assembly, and thermal resistance, K/W belongs to one specific object. Resistance is not conductivity or resistivity: R = L ÷ (k × A) for a slab.
- Temperature interval vs temperature: a difference of 10 °C is a difference of 18 °F. A reading of 10 °C is 50 °F. Every unit here that contains “per degree” or “K” uses intervals, so no offset is ever applied.
Each converter changes units within one quantity only. Related tools: Temperature Interval, Thermal Expansion, Thermal Resistance, Thermal Conductivity, Specific Heat Capacity, Heat Density, Heat Flux Density, Heat Transfer Coefficient, Fuel Efficiency - Mass and Fuel Efficiency - Volume.