Shear rate is a measurement used to describe the movement of fluid through a channel. Specifically, it expresses the fluid's change in speed, known as its velocity gradient. Being able to calculate shear rate is useful because it will allow you to predict the behavior of a fluid more precisely. It also helps you make more informed decisions regarding the best type of channel to use in construction projects.

Determine the velocity of the fluid. This is the speed at which the fluid is flowing through the channel. The measurement should be taken in meters per second.

Determine the height of the channel. This is the distance between the two interior sides of the channel's top and bottom plate.

Divide the velocity by the height. The result is the shear rate. For example, if you had a velocity of 6 meters per second and a height of 2 meters, divide 6 by 2 to get a shear rate of 3 meters per second.
References
 Photo Credit water splash  bottle and water in a moment image by Stasys Eidiejus from Fotolia.com