Inputs

Viscosity input

Velocity

Velocity unit

Characteristic diameter

Diameter unit

Density

Used only with dynamic viscosity.

Density unit

Dynamic viscosity

1 cP is approximately water near room temperature.

Viscosity unit

Results

Reynolds number

—

Flow regime

—

Dimensionless

Re

Equations

Dynamic viscosity: Re = ρVD / μ
Kinematic viscosity: Re = VD / ν

This calculator classifies internal pipe flow as laminar for Re ≤ 2300, transition for 2300 < Re < 4000, and turbulent for Re ≥ 4000. The transition region is inherently less predictable.