Reynolds Number Calculator

How to calculate the Reynolds number

1. Choose a fluid, or Other and enter its density and viscosity.
2. Enter the velocity and the diameter or characteristic length.
3. See the Reynolds number and whether pipe flow is laminar or turbulent.

Frequently asked questions

What values mean laminar or turbulent?

In pipes, flow is usually laminar below about 2,300, turbulent above about 4,000 and transitional in between.

What is the formula?

Re = ρ × v × D / μ: density times velocity times diameter, divided by the dynamic viscosity.

Why does the Reynolds number matter?

It tells whether flow is smooth or turbulent, which changes the pressure drop, heat transfer and mixing.