Pipe velocity converter
Convert a flow rate into the velocity inside the pipe. Pick the bore first: the same flow is gentle in a big pipe and erosive in a small one.
That's 2.7× as fast as the erosive limit — nothing on our list beats it. Getting water moving that fast costs about 9,492 mm of head.
What it means
How fast is it moving?
Velocities are averages across the bore. At the wall the fluid is stationary and in the middle it moves faster, which is what erodes bends.
Every unit
Your velocity in every unit
Learn
Three things worth knowing
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Velocity = flow ÷ area
10 m³/h through a 27 mm bore is 4.8 m/s, which is far too fast. Through a 53 mm bore the same flow is a comfortable 1.3 m/s.
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Why the square matters
Doubling the bore quadruples the area, so the velocity drops to a quarter and the friction loss to about a thirtieth. One pipe size up is usually cheaper than a bigger pump.
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Nominal size is not bore
A "DN50" pipe has a 53 mm bore, not 50. Using the nominal figure understates the area and overstates the velocity by about 10%.
Shortcuts
Popular velocity conversions
Background
About pipe velocity
Pipe sizing is really velocity sizing. Below about 0.5 m/s solids settle out; above 3 m/s water erodes bends and makes noise. Most designs aim for 1 to 2 m/s.
Velocity is flow divided by area, and because area goes with the square of the bore, halving the pipe size quadruples the velocity.