Reynolds Number Calculator
Predicts whether a flow is smooth or turbulent.
Reynolds number
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Share sends a link that reopens these numbers. Copy details pastes the full breakdown as a list.
Kinematic viscosity — m²/s
In a round pipe —
The formula
Re = ρ v L ÷ μ
The ratio of inertia to viscous forces. It has no unit, as long as everything is in consistent units.
What to watch out for
Use the inside diameter for a pipe, and the length along the flow for a flat plate.
Frequently Asked Questions
What is the Reynolds number of water at 1 m/s in a 50 mm pipe?
About 50,000, so it is turbulent.
Why does the Reynolds number matter?
It decides which friction and drag formulas apply, and allows scale models to be compared with real ones.