Pipe Flow Velocity from Flow Rate
Pipe Flow Velocity from Volumetric Flow Rate
Sizing a pipe starts with the continuity equation: for a given flow rate, a smaller pipe means a faster (and more erosive, more lossy) velocity. This worksheet converts a volumetric flow rate into a mean velocity.
From continuity Q = A·v, so v = Q/A with A = πD²/4 for a round pipe.
Inputs
Q := 0.05 m^3/s=0.05 m^3/s
D := 150 mm=150 mm
Area and velocity
A := pi·D^2/4=0.02 m^2
v := Q/A=2.83 m/s
Results
Compare the velocity against accepted design ranges — commonly about 1–3 m/s for water in distribution mains. Velocities that are too high cause noise, erosion and excessive friction loss; too low risks sediment settling.
Assumptions & limitations
- Pipe running full with steady flow.
- Mean velocity — the centreline value is higher.
- Round cross-section; use the actual area otherwise.