Water hydraulics
Pipe velocity
- where
- mean velocity (m/s)
- volume flow (m³/s; any unit you pick is converted)
- internal pipe diameter (m; any unit you pick is converted)
Explain this equation
Works out the average speed of water in a pipe from the flow and bore. Use it to check pipes are not running too fast and noisy, or too slow.
q is the volume flow. d is the internal bore. π × d² / 4 is the cross-sectional area of the bore.
Velocity is flow divided by area. Writing the area of a circle in terms of diameter gives the 4 and π in the equation.
Sense check: 12 L/min in a 20 mm bore is about 0.64 m/s. Halve the bore and velocity goes up four times, because area depends on diameter squared.
Watch out: use the actual internal bore, not the nominal pipe size. The calculator does not set velocity limits.
Enter your values to see the result.
Good to know
Use actual internal bore. This does not establish an allowable noise, erosion or pressure-loss limit.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.