The velocity of flow is a vector quantity given by the magnitude of flow (in m/s) and the direction of flow. Within water conveyances, the average direction of flow at any section normally coincides with the direction of the conveyance centreline, so the velocity is simply given as the magnitude of the flow (essentially, the speed of flow).

The velocity varies within the cross section of a water conduit, being zero at the walls and a maximum near the centroid of the section.

The average velocity, v (m/s) is equal to the flow rate, Q (m³/s) divided by the cross sectional area of the conduit, A (m²), that is:

v = Q / A