Heat Transfer Calculator (Fourier's Law)
Compute the steady-state conductive heat flow through a flat wall from its thermal conductivity, area, temperature difference and thickness.
How to Use the Heat Transfer Calculator (Fourier's Law)
- Look up thermal conductivity k for your material.
- Enter the area and the temperature difference across the wall.
- Enter the wall thickness in millimetres.
- Click Calculate to see heat flow in watts and kilowatts.
Use Cases
- •Insulation sizing for walls, ceilings and ducts.
- •Heat-loss estimates in building envelopes.
- •Physics and thermodynamics homework.
Formula
Fourier's law of heat conduction: Q = k · A · ΔT / L, where k is thermal conductivity (W/m·K), A is area, ΔT is the temperature difference and L is the thickness.
Frequently Asked Questions
What value of k should I use?
Typical mineral wool is 0.035–0.045, brick 0.6–0.8, reinforced concrete 1.7, window glass 1.0, softwood 0.13 W/m·K. Use the manufacturer datasheet for insulation products.
Does this account for convection and radiation?
No. It is the pure conduction term. For a full building-envelope calculation you also need the inside and outside surface heat-transfer coefficients.
Celsius or Kelvin?
For a difference they are numerically identical. You can enter ΔT in °C directly.