Reynolds Number Calculator

Calculate Reynolds number to determine flow regime.

Enter Fluid Properties

Choose a fluid preset or enter custom values

Fluid Preset

Density (ρ)

kg/m³

Flow Velocity (v)

m/s

Characteristic Length (D) — Pipe Diameter

Dynamic Viscosity (μ)

Pa·s

Reynolds Number

Enter your fluid parameters above and tap Calculate to see the Reynolds number.

Reynolds Number Formula

Re = (ρ × v × D) / μ

Re: Reynolds number (dimensionless)
ρ: Fluid density (kg/m³)
v: Flow velocity (m/s)
D: Characteristic length (m)
μ: Dynamic viscosity (Pa·s)

Flow Regime Classification

Re < 2,300: Laminar flow (smooth, predictable)

2,300 ≤ Re < 4,000: Transitional flow

Re ≥ 4,000: Turbulent flow (chaotic, mixing)

Related Calculators

Practical Implications

Laminar flow: Low energy loss, predictable patterns, easier to model.

Turbulent flow: Better mixing, higher friction/drag, requires empirical correlations.

Transitional: Unstable regime, design for either laminar or turbulent to avoid.

Pro Tips

Results update as you type — change any field to see the effect immediately.

Check that every value uses the same unit before comparing results.

Use the copy button to paste the reynolds number figures into a note or spreadsheet.

Nothing is sent to a server, so you can use this with private figures.