To perform a simple flow calculation, multiply the flow area by the flow velocity to determine the flow rate. Ensure that the units of length are consistent when performing calculations. If, for example, the flow area is measured in square meters, the flow rate should be expressed in meters per second. To determine flow rate based on the capacity of a tank as it fills, divide the capacity of fluid stored by the time storage takes.
The equation of continuity states that the flow rate of liquid into a given cross-sectional area of a pipe must equal the flow rate out of that same area. This is true because liquids cannot be compressed. This is a basic principle in the field of fluid dynamics.
To find the cross-sectional area of a pipe that measures 0.1 by 0.1 meters, multiply the two figures to arrive at an area of 0.01 square meters. If fluid was flowing through this pipe at 30 meters per second, the flow rate would be calculated by multiplying 0.01 square meters by 30 meters per second to arrive at a flow rate of 0.3 cubic meters per second.
If a 10 cubic meter tank is filled with fluid over a period of 50 seconds, the flow rate is 10 cubic meters divided by 50 seconds, or 0.2 cubic meters per second.