MihsabaHow to use
Reynolds number Re is dimensionless and compares inertial with viscous effects in a flow. Use Re=ρvL/μ with density and dynamic viscosity, or Re=vL/ν with kinematic viscosity. The calculator also reports ν and a commonly used circular-pipe flow-regime guide.
- Choose dynamic-viscosity μ or kinematic-viscosity ν mode.
- Enter speed and characteristic length; dynamic mode also needs density.
- Calculate Re and read the pipe-flow guide.
How it is calculated
Example
Example: approximate water with ρ=1000kg/m³, v=1m/s, L=0.1m and μ=0.001Pa·s gives Re=100,000.
Important notes
The 2300 and 4000 thresholds shown here are common guidelines for internal circular-pipe flow, not universal boundaries for every geometry or external flow. Correct characteristic length and fluid properties at the actual temperature matter.
Frequently asked questions
What are the units of Reynolds number?
It has no units; it is dimensionless.
How are μ and ν related?
Kinematic viscosity ν=μ/ρ.
Does Re>4000 always mean turbulent?
No. That threshold is only a common circular-pipe guide; transition depends on geometry and conditions.
Is this calculator free?
Yes. It is free to use and requires no account.