Reynolds Number Calculator
Calculate Reynolds Number
Formula
Re = ρvD/μ, where ρ is density, v is velocity, D is characteristic diameter, and μ is dynamic viscosity. Laminar < 2300, Transition 2300–4000, Turbulent > 4000.
Frequently Asked Questions
What does the Reynolds number tell us?
The Reynolds number predicts flow regime: laminar (Re < 2300), transitional (2300 ≤ Re ≤ 4000), or turbulent (Re > 4000) for pipe flow.
What is dynamic viscosity?
Dynamic viscosity (μ) measures a fluid's resistance to shear stress. Water at 20°C has μ ≈ 0.001 Pa·s. Air at 20°C has μ ≈ 1.81 × 10⁻⁵ Pa·s.