Water hydraulics
Flow from bore and velocity
- where
- volume flow (m³/s; the calculator shows L/min)
- internal pipe diameter (m; any unit you pick is converted)
- mean velocity (m/s)
Explain this equation
Works out the volume flow from the internal bore and the average velocity. Use it to find how much a pipe carries at a given velocity.
d is the internal bore. π × d² / 4 is the cross-sectional area. v is the average velocity across the bore.
Flow is area times velocity: every second, a column of water one velocity long passes through the section. The calculator works in m³/s and shows L/min.
Sense check: a 20 mm bore at 1 m/s carries about 19 L/min. Double the bore and the flow at the same velocity goes up four times.
Watch out: this assumes incompressible liquid and average velocity. Use the true internal bore.
Enter your values to see the result.
Good to know
Incompressible mean-flow relationship.
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.