Home ⺠Fluid & Pump ⺠Reynolds Number
Reynolds Number Calculator
Enter velocity, diameter, density and viscosity â Re updates instantly.
Formula
Re = Ï Â· v · D / ÎŒ
Flow Regimes (pipe flow)
| Re | Regime | Friction factor |
|---|---|---|
| < 2300 | Laminar | f = 64/Re |
| 2300 â 4000 | Transitional | unstable â avoid in design |
| > 4000 | Turbulent | f â 0.3164/Re0.25 (Blasius) |
Typical Viscosities (cP, 20 °C)
| Fluid | Ό |
|---|---|
| Water | 1.0 |
| Gasoline | 0.6 |
| Diesel | 3.5 |
| SAE 30 oil | 350 |
| Glycerin | 1400 |
FAQ
What is the Reynolds number physically?
The ratio of inertial to viscous forces â it predicts whether flow is smooth (laminar) or chaotic (turbulent).
What Re is turbulent?
Above ~4000 in pipes. Between 2300 and 4000 the flow is transitional and unpredictable.