Convective Heat Transfer Calculator
Convective heat transfer is how a surface exchanges heat with a moving fluid such as air or water, and Newton's law of cooling gives the rate of that exchange. The heat transfer rate equals the convective heat transfer coefficient times the surface area times the temperature difference between the surface and the fluid. A larger coefficient, which depends on the fluid and how fast it moves, a larger area, or a bigger temperature difference all increase the heat flow. This calculator takes the heat transfer coefficient in watts per square meter per kelvin, the surface area in square meters and the temperature difference in kelvin or degrees Celsius, then returns the heat transfer rate in watts to two decimal places. Because a one-kelvin change equals a one-degree-Celsius change, you can use either for the temperature difference. The relationship is the standard convective form taught in heat transfer and used in everything from heat exchanger design to building energy estimates. Heat transfer and energy efficiency references are published by the US Department of Energy. Every figure is computed deterministically from the formula, shown below, with a worked example that reconciles exactly to the calculator so you can follow each step yourself and check the arithmetic.
Convective heat transfer rate equals Q = h A dT. With a coefficient of 25 W/m2K, an area of 2 m2 and a 40 K temperature difference, the heat rate is 2,000.00 W (2 kW).
Convective heat transfer formula
Q = h A dT
Q = heat transfer rate (W)
h = convective coefficient (W/m2K)
A = surface area (m2), dT = temperature difference (K)
Multiply the heat transfer coefficient by the surface area and by the temperature difference between the surface and the surrounding fluid. The result is the rate of heat flow in watts. Because a kelvin and a degree Celsius are the same size, the temperature difference can be entered in either unit.
Worked example
A surface with a convective heat transfer coefficient of 25 W/m2K and an area of 2 m2 sits 40 K hotter than the surrounding air.
- Multiply h by A: 25 x 2 = 50
- Multiply by the temperature difference: 50 x 40 = 2,000
- The heat transfer rate is 2,000 W
- That is equivalent to 2 kW of heat flow
So the surface loses heat at a rate of 2,000.00 W. These are the calculator's default inputs, so the result above matches the widget exactly.
Convective Heat Transfer Calculator: frequently asked questions
How do you calculate convective heat transfer?
Use Newton's law of cooling: Q = h A dT, where h is the convective heat transfer coefficient, A is the surface area and dT is the temperature difference between the surface and the fluid. With h = 25, A = 2 and dT = 40, the heat rate is 2,000 W.
What is the convective heat transfer coefficient?
It is a measure of how readily heat moves between a surface and a moving fluid, in watts per square meter per kelvin. It depends on the fluid, the flow speed and the surface geometry. Forced convection of water gives a much higher coefficient than still air.
Can I use Celsius for the temperature difference?
Yes. A temperature difference of one kelvin equals a difference of one degree Celsius, so a 40 K difference and a 40 degree Celsius difference are identical. Only differences are used here, not absolute temperatures.
How is convection different from conduction?
Conduction transfers heat through a solid or stationary fluid by direct molecular contact, following Fourier's law. Convection transfers heat between a surface and a moving fluid, and is described by Newton's law of cooling, Q = h A dT.
What is the convective heat transfer formula?
The heat transfer rate is Q = h A dT, the product of the convective coefficient, the area and the temperature difference.
Official sources
- Heat transfer and energy efficiency reference: US Department of Energy (DOE). As at 25 June 2026.
Reviewed by the CalculatorHub team, edited by James Graham, 25 June 2026. See our methodology. This is general information, not financial, tax, legal or investment advice.