Fluid Mechanics
Reynolds Number Calculator
The Reynolds number is a dimensionless quantity that predicts the flow regime in a pipe. It compares inertial forces to viscous forces. This calculator supports both dynamic viscosity and kinematic viscosity formulations for internal circular pipe flow.
TypeInteractive engineering calculator
Calculator
Result
Reynolds number50000
Flow regimeTurbulent
Formulas
Using dynamic viscosity
Re = ρ × v × D / μ
Using kinematic viscosity
Re = v × D / ν
Diagram
Worked example
Water flows in a pipe: ρ = 1000 kg/m³, v = 1 m/s, D = 0.05 m (50 mm), μ = 0.001 Pa·s. What is the Reynolds number?
- 01Re = ρ × v × D / μ
- 02Re = 1000 × 1 × 0.05 / 0.001
- 03Re = 50,000
- 04Re > 4000 → Turbulent flow
Result
The Reynolds number is 50,000. The flow regime is turbulent.
FAQ
Does this calculate pressure drop?
No. Pressure drop requires friction factor, pipe length, and fittings data. This calculator only computes the Reynolds number.
Does this calculate friction factor or use the Moody chart?
No. Friction factor and Moody chart lookup are not implemented.
Does this use pipe roughness?
No. Pipe roughness is relevant to friction factor, not to the Reynolds number calculation itself.
What are the flow regime thresholds?
Laminar: Re < 2300. Transitional: 2300 ≤ Re ≤ 4000. Turbulent: Re > 4000. These are conventional approximations for internal pipe flow.
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