Calculate the convective heat transfer coefficient h = Q/(AÃŽâ€ÂÂÂÂT) from the heat transfer rate, surface area, and temperature difference, or solve for heat rate, area, or temperature difference instead.
Enter the heat transfer rate, surface area, and temperature difference between the surface and the fluid. The convective heat transfer coefficient describes how effectively a fluid carries heat away from (or to) a surface.
The total rate of heat transferred, in watts.
The area of the surface in contact with the fluid, in square meters. Must be greater than 0.
The difference between the surface temperature and the fluid temperature, in kelvin or degrees Celsius (a difference is the same in both scales). Must not be 0.
Default example: 500 W, 2 m² surface, 25 K difference — a moderate forced-air convection case, giving h = 10 W/(m²·K).
Already know the heat transfer coefficient? Enter it along with the surface area and temperature difference to compute the resulting heat transfer rate directly.
The convective heat transfer coefficient, in watts per square meter-kelvin.
The area of the surface in contact with the fluid, in square meters.
The difference between the surface temperature and the fluid temperature, in kelvin or degrees Celsius.
Default example: h = 10 W/(m²·K), 2 m² surface, 25 K difference — the same case as the Coefficient tab, giving Q = 500 W.
Already know three of the four quantities? Solve for whichever one is missing — coefficient, heat rate, area, or temperature difference.
The total rate of heat transferred, in watts.
The convective heat transfer coefficient, in watts per square meter-kelvin.
The area of the surface in contact with the fluid, in square meters.
The difference between the surface temperature and the fluid temperature, in kelvin or degrees Celsius.
Default example: solving for surface area at Q = 500 W, h = 10 W/(m²·K), ÃŽâ€ÂÂÂÂT = 25 K gives A = 2 m².
Enter heat transfer rate, surface area, and temperature difference to compute the coefficient.
4 min read3 steps6 terms3 examples6 FAQsQ = h * A * deltaT
The convective heat transfer coefficient h quantifies how effectively a fluid moves heat across a surface.
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Walk-through
How to Use This Calculator
3 steps▸
1
Enter heat rate, area, and temperature difference
On the Coefficient tab, enter the heat transfer rate (Q, in watts), the surface area (A, in square meters), and the temperature difference (ΔT, in kelvin or degrees Celsius) between the surface and the fluid. Results update instantly as you type.
2
Read the heat transfer coefficient
The result card shows the convective heat transfer coefficient h in W/(m²·K) as the headline number, along with the interpretation comparing it to typical still-air and flowing-water ranges.
3
Or switch tabs to solve for a different quantity
Use the Heat Rate tab if you already know h, A, and ΔT and want Q instead. Use the Solve tab to pick any of the four variables — coefficient, heat rate, area, or temperature difference — and solve for it from the other three.
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Reference
Formula & Methodology
2 formulas▸
Convective heat transfer
Q = h * A * deltaT
The heat transfer rate Q equals the convective heat transfer coefficient h times the surface area A times the temperature difference ΔT between the surface and the surrounding fluid.
Solving for the coefficient
h = Q / (A * deltaT)
Rearranging Newton's law of cooling gives the heat transfer coefficient directly from a measured heat rate, area, and temperature difference — the calculator's default mode.
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Glossary
Key Terms Explained
6 terms▸
Heat transfer coefficientA measure, h, of how effectively a fluid transfers heat to or from a surface by convection, in watts per square meter-kelvin (W/m²·K). Higher values mean more effective heat transfer for the same area and temperature difference.
ConvectionHeat transfer between a solid surface and an adjacent moving fluid (liquid or gas). This calculator models the convective component of heat transfer, not conduction or radiation.
Heat transfer rateThe total rate at which thermal energy is transferred, Q, measured in watts. It equals the coefficient times the area times the temperature difference.
Temperature differenceThe difference ΔT between the surface temperature and the bulk fluid temperature that drives convective heat flow. Because it is a difference, it has the same numeric value in kelvin and in degrees Celsius.
Newton's law of coolingThe principle that the rate of heat loss from a body is proportional to the temperature difference between the body and its surroundings — the physical basis for Q = hAΔT.
W/m²KWatts per square meter-kelvin, the SI unit for the heat transfer coefficient. It expresses how many watts of heat cross one square meter of surface for each kelvin of temperature difference.
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Scenarios
Real-World Examples
3 worked examples▸
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HVAC engineer
Forced-air convection over a duct panel
Heat transfer rate 500 WSurface area 2 m²Temperature difference 25 K
With 500 W transferred across a 2 m² panel at a 25 K temperature difference, the coefficient works out to h = 10 W/(m²·K) — typical of moderate forced-air convection.
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Process engineer
Solving for heat rate given a known coefficient
Heat transfer coefficient 150 W/(m²·K)Surface area 1.5 m²Temperature difference 40 K
A water-cooled coefficient of 150 W/(m²·K) over 1.5 m² with a 40 K difference gives Q = 9,000 W — showing how much more heat liquid convection carries than air at the same area and ΔT.
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Student comparing convection regimes
Typical h values by fluid
Still air 5-25 W/(m²·K)Flowing water 500-10,000 W/(m²·K)
Still air convects heat at only 5-25 W/(m²·K), while flowing water reaches 500-10,000 W/(m²·K) — two to three orders of magnitude higher, which is why liquid cooling is so much more effective than air cooling for the same surface area.
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Deep Dive
Understanding the Convective Heat Transfer Coefficient
The convective heat transfer coefficient h quantifies how effectively a fluid moves heat across a surface. This calculator computes h from a measured heat transfer rate, surface area, and temperature difference, or solves for any one of the four quantities in Q = hAΔT given the other three.
How the calculator works
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Newton's law of cooling states that the rate of convective heat transfer Q is proportional to the surface area A and the temperature difference ΔT between the surface and the fluid, with the constant of proportionality being the heat transfer coefficient h: Q = hAΔT. Rearranged, h = Q/(AΔT) lets you back out the coefficient from a measured or specified heat rate. The same equation, rearranged differently, solves for heat rate, area, or temperature difference when the other three values are known.
Inputs and what they mean
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Heat transfer rate (Q) is the total thermal power moving across the surface, in watts. Surface area (A) is the area in contact with the fluid, in square meters, and must be greater than zero. Temperature difference (ΔT) is the gap between the surface and the fluid temperature, in kelvin or degrees Celsius — since it is a difference, the two scales give the same number, but it must not be zero or the coefficient is undefined. The resulting coefficient h is expressed in watts per square meter-kelvin.
Limits and edge cases
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This calculator assumes a single, uniform coefficient over the whole surface and a fixed temperature difference — real convective flows often have a coefficient that varies with fluid velocity, surface geometry, and whether the flow is laminar or turbulent, and detailed correlations (like the Nusselt number relations) are needed to predict h from first principles rather than back-calculate it. It also does not separate forced convection (fan- or pump-driven flow) from natural convection (buoyancy-driven flow), which typically produce very different coefficients for the same fluid, nor does it account for radiative or conductive heat transfer occurring alongside convection.
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Questions
Frequently Asked Questions
6 questions▸
What is the formula for the heat transfer coefficient?+
The convective heat transfer coefficient is h = Q/(AΔT), where Q is the heat transfer rate in watts, A is the surface area in square meters, and ΔT is the temperature difference between the surface and the fluid.
What units does this calculator use?+
Enter heat transfer rate in watts (W), surface area in square meters (m²), and temperature difference in kelvin or degrees Celsius (K or °C — a difference reads the same in both). The result is in watts per square meter-kelvin, W/(m²·K).
Why is the coefficient so much higher for water than for air?+
Liquids like water conduct and carry heat far more efficiently than gases. Still air typically gives a coefficient around 5-25 W/(m²·K), while flowing water can reach 500-10,000 W/(m²·K), which is why liquid cooling systems are so much more effective at the same surface area.
Can this calculator solve for the heat transfer rate instead of the coefficient?+
Yes. Use the Heat Rate tab to compute Q directly from a known coefficient, area, and temperature difference, or use the Solve tab to choose heat rate (or area, or temperature difference) as the unknown.
What does 'convective' mean in this context?+
Convective heat transfer is heat carried between a solid surface and a moving fluid — air blowing over a hot pipe, or water flowing through a heat exchanger. This calculator computes the coefficient for that convective process specifically, not conduction through a solid or radiative heat transfer.
Does forced convection give a different coefficient than natural convection?+
Yes. Forced convection (driven by a fan or pump) generally produces a much higher heat transfer coefficient than natural convection (driven only by buoyancy from temperature differences) for the same fluid and surface, because the forced flow moves more fluid past the surface per second.
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