Reynolds Number Calculator
Velocity (m/s)
Diameter (m)
Density (kg/m³)
Viscosity (Pa·s)
The Reynolds number (Re) predicts whether fluid flow is laminar (smooth, Re < 2,300) or turbulent (chaotic, Re > 4,000). It is dimensionless and fundamental to fluid dynamics.
- 1Re = ρ × v × d / μ
- 2ρ = density (kg/m³); v = velocity (m/s); d = diameter (m); μ = dynamic viscosity (Pa·s)
- 3Water at 20°C: μ ≈ 0.001 Pa·s
- 4Air at 20°C: μ ≈ 1.81×10⁻⁵ Pa·s
Water at 0.5m/s in 5cm pipe=Re = 998 × 0.5 × 0.05 / 0.001 = 24,950 — Turbulent
| Re | Flow type | Characteristics |
|---|---|---|
| < 2,300 | Laminar | Smooth, predictable, low friction |
| 2,300–4,000 | Transitional | Unstable, mixed |
| > 4,000 | Turbulent | Chaotic, high mixing, higher friction |
References
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