Reynolds Number Calculator: The Universal Flow Classifier
Used by engineers in oil & gas, water treatment, aerospace, and HVAC worldwide, our Reynolds number calculator predicts flow behavior with precision.
How the Reynolds Number Calculator Works
The dimensionless Reynolds number (Re) is defined as:
Re = (v × D) / ν
where ν = μ / ρ (kinematic viscosity)
Our Reynolds number calculator uses exact SI units and real fluid properties.
Reynolds Number Calculator: Flow Regimes
Laminar Flow
Re < 2,300 — Smooth, layered flow. Use Darcy friction factor.
Transitional Flow
2,300 ≤ Re ≤ 4,000 — Unstable, unpredictable.
Turbulent Flow
Re > 4,000 — Chaotic, use Moody chart or Colebrook equation.
Critical Values
Open channel: Re > 500 (turbulent), Re < 500 (laminar).
Reynolds Number Calculator: Standard Fluid Properties
| Fluid | Temperature | ρ (kg/m³) | μ (Pa·s) | ν (m²/s) |
|---|---|---|---|---|
| Water | 20°C | 998.2 | 0.001 | 1.004×10⁻⁶ |
| Air | 20°C | 1.204 | 1.81×10⁻⁵ | 1.50×10⁻⁵ |
| Engine Oil | 20°C | 888 | 0.85 | 9.57×10⁻⁴ |
| Seawater | 15°C | 1025 | 0.0011 | 1.07×10⁻⁶ |
Reynolds Number Calculator: Hydraulic Diameter
For non-circular ducts:
Examples: Rectangle: Dₕ = 2wh/(w+h) | Open channel: Dₕ = 4Rₕ
Applications of the Reynolds Number Calculator
- Pipe Sizing: Determine friction losses
- Pump Selection: Match flow regime
- Heat Exchanger Design: Turbulent for high h
- Water Distribution: Avoid laminar stagnation
- Aerodynamics: Re matching for scale models
- Blood Flow: Re in arteries (pulsatile)
Pro Tips for Using the Reynolds Number Calculator
- Use hydraulic diameter for non-circular sections
- Re > 10⁵ → Fully turbulent (rough pipes)
- Temperature matters: μ decreases with T
- Open channels: Use mean velocity and depth
- Compressible flow: Use local density
- Verify with Moody diagram for pressure drop
Master Fluid Flow
From microfluidics to megaflow pipelines, our Reynolds number calculator ensures optimal design worldwide.
Calculate Re