Keeping velocities in the right range avoids noise, erosion and water hammer in pressurised pipes (usually 1–3 m/s for water) while preventing sediment build-up in drains.
How to use the Pipe Velocity Calculator
- Flow rate Q
- Inner diameter d
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the flow rate and the pipe’s inner diameter.
Inputs explained
| Field | What to enter |
|---|---|
| Flow rate Q | Units: L/s, m³/s, m³/h, L/min, US gpm, ft³/s |
| Inner diameter d | Units: mm, cm, m, in, µm |
What each result means
- Flow velocity v = [Flow rate Q]÷(pi×[Inner diameter d]^2÷4)
- Cross-section area = pi×[Inner diameter d]^2÷4
Example values
How the main result changes when Flow rate Q changes and everything else stays at the example values above:
| Flow rate Q (L/s) | Flow velocity v (m/s) |
|---|---|
| 1 | 0.7958 |
| 1.5 | 1.1937 |
| 2 | 1.5915 |
| 2.5 | 1.9894 |
| 3 | 2.3873 |
| 4 | 3.1831 |
Formula
v = Q / (π·d²/4)
Worked example
Inputs — Flow rate Q: 2 L/s; Inner diameter d: 40 mm.
Results — Flow velocity v = 1.59155 m/s; Cross-section area = 12.56637 cm².
Key terms
- Continuity
- Flow rate = area × velocity.
Frequently asked questions
What velocity is recommended for water pipes?
About 1–2.5 m/s for supply lines.
Why avoid high velocities?
Noise, erosion and pressure surges.
Does the pipe material matter?
Not for velocity – only for friction.
How does diameter affect velocity?
Halving the diameter quadruples the velocity.