v = Q / A
v - Average flow velocity
Q - Flow rate
A - Area flowed through
For a circular cross section, the following results are obtained with
A = p / 4 - D2
v = 4 - Q / (p - D2)
D - Diameter of the circular area flowed through (internal pipe diameter)
c or v are usually used as symbols for the average flow velocity. Often v is used for the local velocity, while c is used as a symbol for the mean velocity. The DIN 24260 provides the symbol v for the average speed.
The average flow velocity is an important parameter when selecting the optimum pipe diameter for a new pipeline.