When is it useful?
Nusselt number compares surface convective heat transfer with conduction through the fluid over a chosen length scale. It helps compare heat-transfer conditions when the geometry and definitions are consistent.
Formula and inputs
Enter convective heat-transfer coefficient h in W/(m²·K), characteristic length L in m, and fluid thermal conductivity k in W/(m·K). The coefficient h must come from a measurement or a separate correlation; this calculator does not predict it.
Open this calculatorWorked example
With h = 50 W/(m²·K), L = 0.1 m, and k = 0.6 W/(m·K), Nu = 50 × 0.1 ÷ 0.6 ≈ 8.33. The units cancel when entered consistently.
Interpreting the result
For the same geometry, length definition, and fluid-property basis, a larger Nu indicates a larger convective coefficient relative to conduction. Nu is neither heat flux nor total heat transferred.
Limits and cautions
Choose L for the geometry, such as pipe diameter or distance along a plate. An average Nu based on average h is not directly interchangeable with a local Nu.
Formula and concept reference: University of the Punjab — Heat Transfer lecture notes. We created the sample inputs and calculations for this guide.