Reynolds Number
Flow Regime Classification
Reynolds Number Calculator
Reynolds Number
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Enter values to classify flow regime
Reynolds Number & Flow Regimes
Reynolds Number Definition
Re = (ρ × V × D) / μ
ρ = Fluid density (kg/m³)
V = Velocity (m/s)
D = Characteristic length/diameter (m)
μ = Dynamic viscosity (Pa·s)
V = Velocity (m/s)
D = Characteristic length/diameter (m)
μ = Dynamic viscosity (Pa·s)
Flow Regime Classification (Pipe Flow)
Laminar: Re < 2,300 — Orderly, parallel flow layers
Transitional: 2,300 ≤ Re ≤ 4,000 — Unstable, flow begins to mix
Turbulent: Re > 4,000 — Chaotic, high mixing and friction
Transitional: 2,300 ≤ Re ≤ 4,000 — Unstable, flow begins to mix
Turbulent: Re > 4,000 — Chaotic, high mixing and friction
Dynamic Viscosity of Common Fluids at 20°C
| Fluid | Viscosity (cP) | Viscosity (Pa·s) |
|---|---|---|
| Water at 20°C | 1.002 | 0.001002 |
| Air at 15°C, 1 atm | 0.0182 | 0.0000182 |
| Mineral oil SAE 10 | 100 | 0.1 |
| Mineral oil SAE 30 | 1000 | 1.0 |
| Glycerin | 1500 | 1.5 |
| Honey | 10000 | 10 |
Kinematic Viscosity Relationship
ν = μ / ρ
Alternative Reynolds number form:
Re = (V × D) / ν
ν = Kinematic viscosity (m²/s or Stokes)
Re = (V × D) / ν
ν = Kinematic viscosity (m²/s or Stokes)