Reynolds Number Calculator
Calculate the Reynolds number for fluid flow, which determines whether the flow is laminar, transitional, or turbulent.
Using density (ρ) and dynamic viscosity (μ)
Flow Properties
Fluid Properties
kg/m³
kg/(m·s)
Reynolds Number Results
Enter parameters to calculate Reynolds number
About Reynolds Number
The Reynolds number (Re) is a dimensionless quantity that helps predict flow patterns in different fluid flow situations. It is defined as the ratio of inertial forces to viscous forces within a fluid.
Re = ρvL/μ = vL/ν
Where:
- ρ = fluid density (kg/m³)
- v = flow velocity (m/s)
- L = characteristic length (m)
- μ = dynamic viscosity (kg/(m·s))
- ν = kinematic viscosity (m²/s)
For different geometries, L is:
- Pipe flow: Diameter
- Airfoil: Chord length
- Flat plate: Length from leading edge
- Sphere/cylinder: Diameter
Flow regimes based on Reynolds number:
Internal Flow (pipes, ducts):
- Laminar: Re < 2,300
- Transitional: 2,300 ≤ Re < 4,000
- Turbulent: Re ≥ 4,000
External Flow (airfoils, obstacles):
- Laminar: Re < 3 × 10⁵
- Transitional: 3 × 10⁵ ≤ Re < 5 × 10⁵
- Turbulent: Re ≥ 5 × 10⁵
At higher Reynolds numbers, inertial forces dominate over viscous forces, leading to turbulent flow characterized by chaotic, irregular fluid motions. At lower Reynolds numbers, viscous forces are dominant, resulting in laminar flow with smooth, ordered fluid motion.