Pipe Velocity Calculator
Enter a liquid flow rate in litres per second and the pipe’s true internal diameter in millimetres. The calculator assumes the pipe runs full.
Mean velocity:
Bore area:
A QUICK WALKTHROUGH
How to use this tool
- Enter flow rate in L/s.
- Enter the true internal pipe diameter in mm.
- Calculate mean velocity and circular bore area.
Full-pipe assumption
This calculator uses Q_m³/s = flow/1000, D_m = diameter/1000, area = πD²/4, and mean velocity = Q/area. It reports average velocity across the circular bore.
Use the true bore
Enter the true internal diameter, not a nominal size or outside diameter. Results do not account for fittings, roughness, elevation, or local velocity profiles.
Scope and context
The calculation excludes partially full pipes and open-channel flow. Designers often keep velocity under roughly 2–3 m/s to limit noise and erosion, but appropriate limits depend on the system and applicable code; this result is not a universal pass/fail check.
GOOD TO KNOW
Common questions
What does the calculator assume?
It assumes a circular pipe running full and reports average velocity through its internal bore.
Should I use nominal pipe size?
No. Use the true internal diameter, because wall thickness and pipe type affect the available bore.
Does this handle open-channel flow?
No. Partially full pipes and open-channel flow need a different calculation.