Reynolds Number Calculator (Laminar or Turbulent Flow)
Enter the fluid properties, speed and pipe diameter or length.
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Reynolds Number Calculator (Laminar or Turbulent Flow) by TheCalcTools
How the Reynolds Number Calculator (Laminar or Turbulent Flow) works
The Reynolds number compares inertial forces to viscous forces: Re = ρvD/μ. Low values mean smooth, layered (laminar) flow; high values mean chaotic, turbulent flow.
In round pipes flow is usually laminar below about 2,300 and turbulent above about 4,000. Other shapes (plates, spheres) have different thresholds.
The formula
Worked example
Using the default values shown in the calculator:
| Density (kg/m³) | 998 |
|---|---|
| Flow velocity (m/s) | 1.5 |
| Characteristic length or pipe diameter (m) | 0.05 |
| Dynamic viscosity (Pa·s) | 0.001 |
- Water at 1.5 m/s in a 50 mm pipe: Re = 74,850, Turbulent (above about 4,000).
Result:
| Reynolds number | 74,850 |
|---|---|
| Pipe flow regime | Turbulent (above about 4,000) |
| Kinematic viscosity (mm²/s) | 1.0020 |
Frequently asked questions
Why does it matter?
Friction losses, heat transfer and mixing all change dramatically between laminar and turbulent flow.
Sources and further reading
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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.