Heat Transfer Coefficient Converter
Convert between heat transfer coefficient units — W/(m²·K), BTU/(h·ft²·°F), W/(cm²·K), and more — instantly. Real-time conversion with copy-to-clipboard.
Heat Transfer Coefficient Converter
Enter a value in any unit — see the conversion in all others instantly.
How to Use the Heat Transfer Coefficient Converter
A heat exchanger design specification lists the convective heat transfer coefficient as 5000 BTU per hour per square foot per degree Fahrenheit. Your simulation software requires the value in watts per square metre per kelvin. The numbers are in completely different unit systems and the conversion is not intuitive. Enter the value, pick the source unit, and the converter shows the equivalent in all seven supported heat transfer coefficient units.
An air conditioning coil specification lists the heat transfer coefficient as 50 watts per square metre per kelvin for forced convection across the fins. Enter 50 in W per m squared per K and the converter shows 8.8 BTU per hour per square foot per degree F. This value falls within the typical range of 25 to 250 for forced air systems.
A steam condenser specification lists the heat transfer coefficient as 10,000 watts per square metre per kelvin. Convert to BTU per hour per square foot per degree F and the result is 1763. The converter also shows 2.39 calories per second per square centimetre per degree C for the legacy European specification.
A vehicle cooling system specification lists the heat transfer coefficient as 3000 kilocalories per hour per square metre per degree C. Enter 3000 in kcal per h per m squared per degree C and the converter shows 3488.3 watts per square metre per kelvin. This value is well above the 1000 threshold for effective liquid cooling in automotive applications.
A boiling heat transfer experiment measures the coefficient as 25,000 watts per square metre per kelvin. Convert to watt-hours per square metre per kelvin and the result is 6.94. The converter also shows 4390 BTU per hour per square foot per degree F for the American chemical engineering specification.
How the Heat Transfer Coefficient Converter Works
This tool converts between different units used to express the convective heat transfer coefficient, which relates heat flux to temperature difference between a surface and a fluid. All calculations run instantly in your browser with no data sent to a server.
Heat Transfer Coefficient Units
The heat transfer coefficient is expressed in units of energy per unit time, per unit area, per unit temperature difference. The most common SI unit is W per square metre per kelvin. In imperial systems, BTU per hour per square foot per degree F is widely used. Other units include kcal per hour per square metre per degree C, calorie per second per square centimetre per degree C, and kJ per hour per square metre per kelvin. Each unit pairs a different energy scale with a different area and temperature scale.
Conversion Mathematics
All conversions use W per square metre per kelvin as the base unit. Each unit has a fixed conversion factor. For example, 1 BTU per hour per square foot per degree F equals 5.67447 W per square metre per kelvin. To convert between any two units, the tool multiplies by the source factor and divides by the target factor. The formula is Result = Input x (FromFactor / ToFactor).
Convection vs Radiation Coefficients
The heat transfer coefficient described here applies specifically to convection, heat transfer between a surface and a moving fluid. Radiation heat transfer uses a different formulation based on emissivity and the Stefan-Boltzmann law, though an effective radiation coefficient can sometimes be defined for linearised calculations. Typical convective values range from about 5 W per square metre per kelvin for natural convection in air up to 10,000 plus W per square metre per kelvin for boiling liquids.
Frequently Asked Questions
What is the difference between convection and radiation heat transfer coefficients?
A convection heat transfer coefficient relates heat flux to the temperature difference between a surface and a moving fluid, following Newton's law of cooling. A radiation coefficient is a linearized approximation derived from the Stefan-Boltzmann law and depends on emissivity and temperature. Convection coefficients are typically much higher than radiation coefficients at moderate temperatures.
What are typical heat transfer coefficient values for air vs water cooling?
Natural convection in air typically ranges from 5 to 25 W/(m²·K), while forced convection in air reaches 25 to 250 W/(m²·K). Water is far more effective: natural convection in water is about 100 to 600 W/(m²·K), and forced convection in water ranges from 100 to 2000 W/(m²·K). Boiling water can exceed 10,000 W/(m²·K).
How does surface area affect heat transfer?
Total heat transfer rate equals the heat transfer coefficient multiplied by surface area and temperature difference (Q = h × A × ΔT). A larger surface area increases the total heat transferred for a given coefficient and temperature difference. Fins and extended surfaces are commonly used to increase effective area in heat exchangers and electronics cooling.
Why use different units for the heat transfer coefficient?
Different industries and regions favor different unit systems. W/(m²·K) is the SI standard used in most scientific and engineering contexts. BTU/(h·ft²·°F) is common in HVAC and American engineering practice. kcal/(h·m²·°C) appears in older European and Asian references. Converting between them ensures consistent calculations across documents and standards.
What factors influence the value of the heat transfer coefficient?
The coefficient depends on fluid properties such as thermal conductivity, viscosity, density, and specific heat. Flow conditions — velocity, turbulence, and whether the flow is laminar or turbulent — have a major effect. Surface geometry, roughness, and orientation also influence the coefficient. Phase changes like boiling or condensation dramatically increase heat transfer rates.
How accurate are these unit conversions?
The conversions use exact, internationally recognized conversion factors between unit systems. For example, 1 BTU/(h·ft²·°F) is exactly 5.67447 W/(m²·K). The tool performs arithmetic only — no approximations or assumptions are involved. Results are as accurate as the precision of JavaScript floating-point arithmetic allows.