Thermal diffusivity converter
Convert how fast heat spreads through a material between mm²/s, m²/s and ft²/h.
That's 1.33× as quick to heat through as concrete, while stainless steel is 4.2× quicker. Heat soaks about 1 cm into it in 100 seconds.
What it means
How fast does heat spread?
Values are typical at room temperature. Diffusivity falls in most metals as they heat up.
Every unit
Your diffusivity in every unit
Learn
Three things worth knowing
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Time ≈ distance² ÷ diffusivity
Heat creeps 1 cm into water in about 12 minutes, and 1 cm into copper in about a second. Double the thickness and it takes four times as long.
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Fourier’s other number
Joseph Fourier’s heat equation of 1822 has diffusivity as its only material constant. Everything else about how a shape warms up follows from geometry.
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High conductivity is not the whole story
Air conducts heat badly, yet its diffusivity is higher than steel’s, because there is so little of it to warm. It changes temperature fast; it just carries little heat doing it.
Shortcuts
Popular thermal diffusivity conversions
Background
About thermal diffusivity
Conductivity says how much heat flows; diffusivity says how fast a temperature change travels. It is conductivity divided by how much heat the material soaks up on the way: α = k ÷ (ρ·c).
That is why a copper pan heats evenly in seconds and a steak takes minutes to cook through: copper is about 800 times more diffusive than meat or water.