About the Pipe Flow Calculator
What is the Pipe Flow Calculator?
Getting the pipe size right keeps velocity in a sensible range: too fast causes noise, erosion and water hammer; too slow wastes money on oversized pipe. This pipe flow calculator shows the velocity for a given flow and diameter.
It also gives the Reynolds number, whether flow is laminar or turbulent, and the diameter needed for your preferred velocity.
How to use the Pipe Flow Calculator
- Flow Rate (L/min) (sample: 200)
- Pipe Inner Diameter (mm) (sample: 40)
- Recommended Velocity for Sizing (m/s) (sample: 1.5)
- Press Calculate Pipe Velocity (results also refresh as you type). The result card shows the Flow Velocity, along with Reynolds number (water, 20 °C), Flow regime, Diameter for the recommended velocity and Reading.
Formula used
v = Q ÷ (π × D² ÷ 4)
- Re = v × D ÷ ν, with ν = 1.004 × 10⁻⁶ m²/s for water at 20 °C
- Diameter for velocity v = √(4Q ÷ (π × v))
Domestic water lines are usually designed for 0.6–2 m/s.
Worked example
These are the sample values already filled in the calculator above, and the result it returns for them:
| Input | Sample value |
|---|---|
| Flow Rate (L/min) | 200 |
| Pipe Inner Diameter (mm) | 40 |
| Recommended Velocity for Sizing (m/s) | 1.5 |
| Result | Value |
|---|---|
| Flow Velocity | 2.653 m/s |
| Reynolds number (water, 20 °C) | 1,05,681 |
| Flow regime | Turbulent |
| Diameter for the recommended velocity | 53.2 mm |
| Reading | Within the usual range |
Tips for using the Pipe Flow Calculator
- Pump suction lines should run slower (under about 1.5 m/s) than delivery lines.
- Check pressure loss with the pressure drop calculator for long runs.