What is the Heat Transfer Calculator?

Calculate heat transfer by conduction, convection, and radiation with this free heat transfer calculator. Use Fourier's law Q = kAΔT/L, Newton's law Q = hAΔT, Stefan–Boltzmann radiation Q = εσA(T₁⁴−T₂⁴), overall U-value Q = UAΔT, and composite wall assemblies. Get heat rate in W, kW, and BTU/hr with thermal resistance and heat flux. Material and convection presets included. Metric and imperial units. Runs instantly in your browser.

How to use the Heat Transfer Calculator

Choose Conduction, Convection, Radiation, Overall U-Value, or Composite Wall mode.
Select metric or imperial units.
Enter surface area, temperature difference or absolute temperatures, and material properties.
Use conductivity, convection, or emissivity presets for common materials.
Review heat rate, thermal resistance, U-value, and copy calculation steps.

Common use cases

Estimating heat loss through a wall or window assembly
Sizing a heater for a convective surface
Calculating radiative heat from a hot surface
Finding U-value of an insulated wall layer
Thermodynamics and heat transfer coursework

Frequently asked questions

What is Fourier's law of conduction?: One-dimensional conduction: Q = kAΔT/L, where k is thermal conductivity (W/m·K), A is area, ΔT is temperature difference, and L is thickness. Thermal resistance R = L/(kA) in K/W.
How do I calculate convective heat transfer?: Newton's law of cooling: Q = hAΔT, where h is the convection coefficient (W/m²·K). Natural air is roughly 5–25; forced air 10–100; water can exceed 1000 W/m²·K.
What is the Stefan–Boltzmann equation?: Radiative heat transfer between a surface and surroundings: Q = εσA(T₁⁴ − T₂⁴). Temperatures must be in kelvin; ε is emissivity (0–1); σ = 5.67×10⁻⁸ W/(m²·K⁴).
How is overall U-value calculated for a wall?: For a plane wall with inner and outer convection: U = 1 / (1/hᵢ + L/k + 1/hₒ). Heat loss Q = UAΔT. Lower U means better insulation.
What units does this calculator use for heat rate?: Results are shown in watts (W), kilowatts (kW), and BTU/hr. Imperial inputs use ft, in, ft², and °F; calculations use SI internally for accuracy.

More Scientific Tools

Heat Transfer Calculator

Calculate heat transfer by conduction (Fourier), convection (Newton), radiation (Stefan–Boltzmann), overall U-value, and composite wall assemblies. Enter geometry, temperatures, and material properties — get heat rate in W, kW, and BTU/hr with thermal resistance. Metric and imperial units. Free, browser-based.

What is the Heat Transfer Calculator?

How to use the Heat Transfer Calculator

Choose Conduction, Convection, Radiation, Overall U-Value, or Composite Wall mode.

Select metric or imperial units.

Enter surface area, temperature difference or absolute temperatures, and material properties.

Use conductivity, convection, or emissivity presets for common materials.

Review heat rate, thermal resistance, U-value, and copy calculation steps.

Frequently asked questions

What is Fourier's law of conduction?

One-dimensional conduction: Q = kAΔT/L, where k is thermal conductivity (W/m·K), A is area, ΔT is temperature difference, and L is thickness. Thermal resistance R = L/(kA) in K/W.

How do I calculate convective heat transfer?

Newton's law of cooling: Q = hAΔT, where h is the convection coefficient (W/m²·K). Natural air is roughly 5–25; forced air 10–100; water can exceed 1000 W/m²·K.

What is the Stefan–Boltzmann equation?

Radiative heat transfer between a surface and surroundings: Q = εσA(T₁⁴ − T₂⁴). Temperatures must be in kelvin; ε is emissivity (0–1); σ = 5.67×10⁻⁸ W/(m²·K⁴).

How is overall U-value calculated for a wall?

For a plane wall with inner and outer convection: U = 1 / (1/hᵢ + L/k + 1/hₒ). Heat loss Q = UAΔT. Lower U means better insulation.

What units does this calculator use for heat rate?

Results are shown in watts (W), kilowatts (kW), and BTU/hr. Imperial inputs use ft, in, ft², and °F; calculations use SI internally for accuracy.