Calculate the cross-sectional area of where the liquid passes through. For example, if the fluid's conduit is a circular pipe with a 6-centimeter diameter, halve the length of the diameter and square it. Halving 6 centimeters results in 3 centimeters, and the square of 3 centimeters is 9 centimeters squared.
Multiply that number by pi, which is a mathematical constant approximated by 3.14. Multiplying the previous result by pi results in 28.26 centimeters squared.
Multiply the area by the average flow velocity. For the example, the average flow velocity is 15 centimeters per second. Multiplying 28.26 square centimeters by 15 centimeters per second results in 423.9 cubic centimeters per second.