Heat Transfer Rate Calculator
Find conductive heat flow through a wall.
Material property k.
Thickness of the material the heat crosses.
Results update as you type.
How it works
The heat transfer rate tells you how fast thermal energy conducts through a solid barrier, and this heat transfer rate calculator computes it with Fourier's law from the material's thermal conductivity, the area, the temperature difference across it, and its thickness. The result, in watts, is the steady rate at which heat crosses the barrier from the hot side to the cold side, which sets how quickly a space heats up or cools down. This matters for insulation and thermal design: building walls, refrigerator panels, furnace linings, electronic heat sinks, and clothing all manage heat flow through conduction. Engineers use the heat transfer rate to size insulation, estimate heating and cooling loads, and keep components within temperature limits. A heat transfer rate calculator quickly shows how conductivity, thickness, and area trade off against one another in a design. The formula works because heat conducts faster when the temperature difference driving it is larger, when more area is available, and when the material conducts well, while thicker material lengthens the path and slows the flow. That is why insulation combines low-conductivity materials with generous thickness. Mechanical, building-services, and thermal engineers, along with students, rely on a heat transfer rate calculator to design efficient, comfortable, and safe thermal systems.
Q = k × A × ΔT ÷ thickness
Fourier's law of conduction says the heat flow rate through a material equals its thermal conductivity times the cross-sectional area times the temperature difference across it, divided by its thickness. A bigger temperature gap or larger area drives more heat, a more conductive material passes heat more readily, and greater thickness slows the flow by lengthening the path heat must travel, which is exactly why insulation is made thick and from low-conductivity materials.
Source:Fourier's law of heat conduction
We review all our tools from time to time to ensure accuracy.
Worked example
How to use this calculator
- 1
Enter your values
Enter thermal conductivity, area, temperature difference and thickness.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Heat transfer rate updates instantly as you type — no button to press.
Frequently asked questions
What is Fourier's law of conduction?
Fourier's law states that the rate of heat conduction through a material is proportional to the temperature difference across it and the area, and inversely proportional to the thickness, scaled by the material's thermal conductivity. In steady state it gives heat flow equals conductivity times area times temperature difference divided by thickness. It is the fundamental equation governing how heat moves through solid barriers like walls and insulation.
What is thermal conductivity?
Thermal conductivity, symbol k, measures how readily a material conducts heat, in watts per metre per kelvin. Metals like copper have high conductivity and move heat quickly, while insulators like foam, wood, and air have low conductivity and resist heat flow. It is an intrinsic material property, so choosing a low-conductivity material is one of the main ways to reduce unwanted heat transfer in a design.
How does thickness affect heat transfer?
Thickness appears in the denominator, so doubling the thickness of a material halves the rate of heat conduction through it, all else equal. A longer path gives heat more distance to travel and more resistance to overcome. This is why insulation is made thick: adding material directly reduces heat loss. There are practical and cost limits, so designers balance thickness against space and expense.
What units does this calculator use?
Enter thermal conductivity in watts per metre-kelvin, area in square metres, temperature difference in kelvin, and thickness in metres. The heat transfer rate comes out in watts. Because a temperature difference of one kelvin equals one degree Celsius, you can enter the difference in degrees Celsius directly. Keeping all inputs in these consistent SI units ensures the resulting heat flow is correct.
Does this account for convection and radiation?
No. This calculator handles only conduction, the transfer of heat through a solid material by direct contact. Real systems often also lose or gain heat by convection to surrounding air and by radiation, which follow different laws. For a complete thermal analysis, especially at surfaces exposed to air, you would combine conduction with convective and radiative terms rather than relying on conduction alone.