Nusselt Number Calculator

How to Use Nusselt Number Calculator

Choose mode — Definition, or Dittus–Boelter correlation.
Enter inputs in SI units.
Read Nu in the result panel.

Formula & Theory - Nusselt Number Calculator

Definition:
  Nu = h · L / k

Dittus–Boelter correlation (turbulent pipe flow):
  Nu = 0.023 · Re^0.8 · Pr^n
       n = 0.4  if the fluid is being heated
       n = 0.3  if the fluid is being cooled

Symbol	Meaning
h	Convective heat-transfer coefficient (W/m²·K)
L	Characteristic length, e.g. pipe diameter (m)
k	Fluid thermal conductivity (W/m·K)
Re	Reynolds number
Pr	Prandtl number

Assumptions and Limits

Dittus–Boelter is empirical; ±25 % accuracy is typical.
Valid range: 0.6 < Pr < 160, Re > 10 000, L/D > 10.
For viscous fluids near walls, Sieder–Tate is more accurate.

Use Cases for Nusselt Number Calculator

Heat-exchanger design — Estimate film coefficient before detailed CFD.
Pipe-flow heating — Quick sanity check on h.
Education — Connect Re, Pr to Nu in turbulent flow.

The Nusselt Number Calculator supports both the textbook definition and the Dittus–Boelter correlation.

Frequently asked questions about Nusselt Number Calculator

What is the Nusselt number?

Nu is the dimensionless ratio of convective to conductive heat transfer across a boundary. Nu = 1 means pure conduction; larger Nu means stronger convection.

When should I use Dittus–Boelter?

For fully developed turbulent flow in a smooth pipe with 0.6 < Pr < 160 and Re > 10 000. Use n = 0.4 when the fluid is heated, n = 0.3 when cooled.

How do I get h from Nu?

Once Nu is known, h = Nu · k / L.

Is my data stored?

No. All calculations happen in your browser; nothing is sent to a server.