Low Reynolds numbers mean smooth, layered flow; high values mean chaotic, turbulent flow. In pipes, transition is around 2,300–4,000.
How to use the Reynolds Number Calculator
- Fluid density
- Flow velocity
- Pipe diameter
- Dynamic viscosity
Results update as you type, and every field accepts the units shown in its menu.
How it works
Multiply density, velocity and diameter and divide by dynamic viscosity.
Inputs explained
| Field | What to enter |
|---|---|
| Fluid density | Units: kg/m³, g/cm³, g/mL, lb/ft³ |
| Flow velocity | Units: m/s, km/h, mph, ft/s, knots |
| Pipe diameter | Units: m, cm, mm, km, in, ft … |
| Dynamic viscosity | In Pa·s |
Example values
How the main result changes when Fluid density changes and everything else stays at the example values above:
| Fluid density (kg/m³) | Reynolds number |
|---|---|
| 499 | 37,425 |
| 748.5 | 56,138 |
| 998 | 74,850 |
| 1,247.5 | 93,563 |
| 1,497 | 112,275 |
| 1,996 | 149,700 |
Formula
Re = ρ v D ÷ μWorked example
Inputs — Fluid density: 998 kg/m³; Flow velocity: 1.5 m/s; Pipe diameter: 0.05 m; Dynamic viscosity: 0.001 Pa·s.
Results — Reynolds number = 74,850.
Frequently asked questions
What is water’s viscosity?
About 0.001 Pa·s at 20 °C.
Do the thresholds apply to all shapes?
No, they are for flow in round pipes.
What formula does the Reynolds Number Calculator use?
Re = ρ v D ÷ μ.