Biot Number Calculator

Low Bi lets you treat an object as a single temperature, simplifying cooling calculations.

Find the Biot number for transient heat conduction.

Heat transfer coefficient (W/(m²·K))

Characteristic length

Thermal conductivity (W/(m·K))

Biot number 0.005

Formula: Bi = h·L_c ÷ k

Step-by-step with your numbers:

1. Values used:

2. Heat transfer coefficient = 50 W/(m²·K)

3. Characteristic length = 0.02

4. Thermal conductivity = 200 W/(m·K)

6. Heat transfer coefficient x Characteristic length = 50 x 0.02 = 1

7. Biot number = (Heat transfer coefficient x Characteristic length) / Thermal conductivity = 1 / 200 = 0.005

Did we solve your problem today?

The Biot number tells whether an object heats/cools uniformly or with internal gradients.

The math behind it

Bi = h·L_c ÷ k. Bi < 0.1 means the object stays nearly uniform (lumped capacitance applies).

h 50, L 0.02 m, k 200 → Bi = 0.005 (lumped).

Why does it matter?

Low Bi lets you treat an object as a single temperature, simplifying cooling calculations.