🌡️ Biot Number Calculator
Calculate the Biot number, a dimensionless ratio used in heat transfer to check whether temperature stays roughly uniform inside a solid as it heats or cools.
What the Biot number tells you
The Biot number compares the resistance to heat conduction inside a solid to the resistance to heat convection at its surface. It helps engineers decide whether a simplified ‘lumped capacitance’ model (assuming uniform internal temperature) is accurate enough for a heat transfer problem.
The formula
Biot number Bi = (h × Lc) / k, where h is the convective heat transfer coefficient of the surrounding fluid, Lc is a characteristic length (often volume divided by surface area), and k is the thermal conductivity of the solid. A common rule of thumb is that lumped capacitance analysis is reasonably accurate when Bi < 0.1.
This calculator is intended for general engineering education and preliminary estimates.