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Heat Transfer Calculator
Enter a material's thermal conductivity, thickness, area, and temperature difference to calculate the rate of conductive heat transfer.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Heat transfer rate
—
watts (joules/sec)
Flux density
—
W/m²
Energy per day
—
kWh, running 24h
How the calculation works
- Pick a material preset or enter a custom thermal conductivity (k) in W/m·K.
- Enter the material's thickness, the surface area it covers, and the temperature difference across it.
- The heat transfer rate, flux density, and daily energy loss update instantly as you type.
The formula
Steady-state conduction through a flat material follows Fourier's law:
Q = k × A × ΔT / L
Example: a brick wall (k = 0.7 W/m·K), 100 mm thick, 12 m² of area, with an 18°C difference between inside and outside loses Q = 0.7 × 12 × 18 / 0.1 = 1,512 W — about 36.3 kWh per day if that gradient held constant.
FAQ
What formula does this calculator use?
Fourier's law for steady-state conduction: Q = k × A × ΔT / L, where k is thermal conductivity (W/m·K), A is the surface area in m², ΔT is the temperature difference in °C, and L is the material thickness in meters. It gives the heat transfer rate in watts.
Does this account for convection or radiation?
No — this is a pure conduction calculator for a single flat material layer. Real walls or enclosures also lose heat through convection at each surface and radiation, so a full building heat-loss estimate would need surface film coefficients on top of this number.
Where do I find the thermal conductivity of my material?
Pick one of the built-in presets (insulation, wood, brick, concrete, glass, steel, copper, aluminum) or enter your own k value from a manufacturer datasheet — conductivity varies by density and composition even within one material type, so a datasheet value is more accurate than a generic lookup.
How we compare
| Feature | Online Tool Store | Doing it by hand | Engineering software (e.g. spreadsheet templates) |
|---|---|---|---|
| Instant results as you type | ✓ | ✗ | ✓ |
| Built-in material presets | ✓ | N/A | ✗ |
| Free, no sign-up or spreadsheet license | ✓ | ✓ | ✗ |
For a quick conduction estimate — sizing insulation, sanity-checking a heat-loss claim, or a homework problem — this calculator gets you the same Fourier's-law answer as a spreadsheet in seconds, with no setup.