Reynolds Number Calculator
Evaluate whether a fluid flow is laminar, transitional, or turbulent by calculating its Reynolds number. Enter density, velocity, characteristic length, and dynamic viscosity.
Engineering estimate only. Validate assumptions and units before applying results to critical designs.
Examples
- Water: 997 kg/m³, 1.5 m/s, 0.05 m, 0.001 Pa·s ⇒ 74,775.00 Re
- Air: 1.225 kg/m³, 12 m/s, 0.1 m, 0.0000181 Pa·s ⇒ 81,215.47 Re
FAQ
What ranges define laminar and turbulent flow?
Re < 2,300 is typically laminar, 2,300–4,000 transitional, and > 4,000 turbulent in pipe flow.
Can I enter kinematic viscosity instead?
Convert kinematic viscosity (ν) to dynamic viscosity (μ) by μ = ρ·ν before using this calculator.
Does pipe roughness affect the result?
The Reynolds number itself does not include roughness, but you can use it to select the right friction factor correlation.
Additional Information
- Reynolds number (Re) = (density × velocity × characteristic length) ÷ dynamic viscosity.
- The result is dimensionless and helps select appropriate fluid mechanics models.
- Need deeper guidance? Read the ISO-aligned [Reynolds number explainer](/units-and-measures/reynolds-number-re-inertial-viscous-similarity/) for regime thresholds, property selection tips, and cross-links to Mach and Nusselt scaling.