Heat Transfer Coefficient Calculator

Calculate the convective heat transfer coefficient (h) from heat transfer rate, surface area, and the temperature difference across the surface, using Newton's Law of Cooling.

Quick Facts

Newton's Law of Cooling
Q = h · A · ΔT
Rearranged to solve for the coefficient: h = Q / (A × ΔT).
SI units
W/(m²·K)
US customary units use BTU/(hr·ft²·°F); 1 W/(m²·K) ≈ 0.1761 BTU/(hr·ft²·°F).
Typical ranges
2 to 100,000+ W/(m²·K)
Free convection in air is lowest; boiling and condensation are highest.

Your Results

Calculated
Heat Transfer Coefficient (h)
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h = Q / (A × ΔT), in W/(m²·K)
Heat Transfer Coefficient (h)
-
Same value in BTU/(hr·ft²·°F)
Temperature Difference (ΔT)
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|Hot − Cold|, converted to kelvin
Convection Regime (approximate)
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Typical process matching this h value

Ready

Enter the heat rate, surface area, and both temperatures, then press Calculate.

Formula and Method for the Heat Transfer Coefficient

The convective heat transfer coefficient, h, measures how efficiently heat moves between a solid surface and a moving fluid (air, water, oil, and so on) in contact with it. It is the proportionality constant in Newton's Law of Cooling: Q = h·A·ΔT, where Q is the rate of heat transfer (in watts), A is the surface area in contact with the fluid (in m²), and ΔT is the temperature difference between the surface and the bulk fluid (in kelvin, equivalently degrees Celsius). This calculator rearranges the formula to solve for h directly: h = Q / (A × ΔT).

How the calculation works

Enter the heat transfer rate Q and choose its unit (watts, kilowatts, or BTU/hour), enter the surface area A and its unit, and enter the hot-side and cold-side temperatures with their shared unit. The calculator converts Q to watts and A to square meters, takes the absolute difference between the two temperatures and converts it to kelvin (a 1°C difference equals a 1 K difference; a 1°F difference equals 5/9 K), then divides: h = Q / (A × ΔT). The result is also converted to BTU/(hr·ft²·°F) for engineers working in US customary units.

Common mistakes

  • Confusing ΔT with absolute temperature: h depends on the temperature difference, not the absolute surface temperature. A hot surface at 90°C next to a 25°C fluid has ΔT = 65°C (65 K), not 90°C or 363 K.
  • Treating h as a fixed material property: unlike thermal conductivity, h is not a material constant — it depends on fluid velocity, viscosity, density, and geometry, and whether convection is natural or forced, so the same surface can have very different h values under different conditions.
  • Mixing unit systems mid-calculation: keep Q, A, and temperature units consistent with the selectors above; the calculator converts internally, but manual cross-checks should use one consistent set of base units throughout.

Real-world applications

  • HVAC and building design use h to size radiators, baseboard heaters, and convectors, and to estimate heat loss through walls and windows.
  • Electronics cooling uses h to determine whether natural convection is sufficient or whether a fan (forced convection) is needed to keep components below a safe operating temperature.
  • Heat exchanger design combines the convective coefficients on both sides of a wall with the wall's conductive resistance to find the overall heat transfer coefficient U.
  • Process engineering uses measured or correlated h values (from Nusselt number correlations) to size boilers, condensers, and industrial heating and cooling equipment.

Frequently Asked Questions

What is the heat transfer coefficient?
The heat transfer coefficient (h) measures how effectively heat moves by convection between a solid surface and a moving fluid such as air or water. It is the proportionality constant in Newton's Law of Cooling, Q = h·A·ΔT, where Q is the heat transfer rate in watts, A is the surface area in contact with the fluid, and ΔT is the temperature difference between the surface and the fluid. A higher h means more heat moves per unit area per degree of temperature difference.
What is a typical value for the heat transfer coefficient?
Typical convective coefficients range from about 2-25 W/(m²·K) for free (natural) convection in air, 25-250 W/(m²·K) for forced convection in air or gas, 50-20,000 W/(m²·K) for forced convection in water, and 2,500-100,000 W/(m²·K) for boiling or condensing fluids. The wide range reflects how strongly fluid motion, fluid type, and phase change affect convective heat transfer.
How is the heat transfer coefficient different from thermal conductivity?
Thermal conductivity (k, in W/(m·K)) is a material property describing conduction through a solid or stationary fluid. The heat transfer coefficient (h, in W/(m²·K)) describes convection at a surface-fluid boundary and depends on fluid velocity, viscosity, density, and geometry, not just the material — it is usually found experimentally or from Nusselt number correlations, not a material lookup table.
How does h relate to the overall heat transfer coefficient U used in heat exchangers and walls?
For a wall or heat exchanger separating two fluids, the overall heat transfer coefficient U combines the convective coefficients on each side (h1, h2) with the conductive resistance of the material between them: 1/U = 1/h1 + L/k + 1/h2, where L is wall thickness and k is thermal conductivity. U is always smaller than the smallest individual h in the series because resistances add.

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