MAXScanner thermal & fluid engineering
Biot Number Calculator — Lumped-Capacitance Validity Check
Calculate Biot number from convection coefficient, characteristic length and solid thermal conductivity, with a lumped-model guide.
Last updated: September 17, 2026
Results
Enter non-negative h/L and positive conductivity
Formula, example and assumptions
Bi=hL_c/k_s.
h=20 W/m²K, Lc=0.01 m and k=50 W/mK gives Bi=0.004.
- Lc is commonly volume divided by convecting surface area.
- Bi<0.1 is a common guide, not a universal accuracy guarantee.
Frequently asked questions
Why is Biot number useful?
It compares internal solid conduction resistance with external convection resistance.
When is lumped capacitance reasonable?
A common first check is Bi below about 0.1.