Pipe flow velocity calculator
Water velocity in a pipe from flow rate and inner diameter.
Fill in the fields and the result will appear here automatically.
Convert volume flow into mean velocity through a circular cross-section: v=Q/A. Use inner diameter and volume flow at conditions in that section. Local velocity within the profile may differ from the mean. The result does not specify an acceptable bore, noise limit or flow regime; those need fluid and system properties.
How it works
Formula and logic
Velocity = flow rate / cross-section area, area = πd²/4.
Example
10 m³/h through a 50 mm inner diameter gives 1.415 m/s.
Fields and units
- Flow rate — m³/h
- Inner diameter — mm
How to use
- — Use the INNER diameter: on polypropylene and multilayer pipe it is noticeably smaller than the outer.
- — Flow rate is in cubic metres per hour — the unit pumps and meters are rated in.
- — There is no single normal speed for all pipes. Requirements depend on fluid, temperature, material, purpose, head loss and noise. This page supplies mean velocity; compare it with the requirements of the particular system, not an automatic threshold.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- OpenStax: volume flow and mean speed
- Limitation
- Mean velocity from positive volume flow and a circular inner section. Viscosity, velocity profile, Reynolds number, head loss and acoustics are not computed. This formula provides no universal 2 m/s limit.
FAQ
What velocity is normal?
There is no single normal speed for all pipes. Requirements depend on fluid, temperature, material, purpose, head loss and noise. This page supplies mean velocity; compare it with the requirements of the particular system, not an automatic threshold.
Why the inner diameter specifically?
Because that is where the water goes. A polypropylene pipe with a 32 mm outer diameter may have a 21 mm bore — 2.3 times less area and 2.3 times the velocity you would get from the outer figure.
How do I bring the velocity down?
Increase the diameter. Area grows as the square: going from 50 to 63 mm cuts velocity by about 1.6 times. Reducing the flow is usually not an option — the consumers set it.
Is head loss included?
No. Losses need length, roughness, viscosity and fittings. A result v=Q/A alone does not prove that the bore is undersized, and 2 m/s alone does not predict noise.