The flow rate through any filter should not exceed the filter's capacity to handle the water. Filter areas are calculated to handle the maximum possible flow of water through the system. 
Manufacturer's develop specifications for the amount of water flow through the filter in question. These specifications are governed by standards as established by the National Sanitation Foundation International (NSFI). These standards are referred to as Filter Media Rate also known as FMR. The chart shows the FMR for the various filter types. 
Formulas:

Examples:

We will continue to use a series of "plugand play" boxes as they are applied in the CPO^{®} class. Just plug the correct number as given by the problem a perform the math (play) as indicated. 

FR = x = 
Just as a reminder, knowing how to calculate area is important for determining heat loss, sizing pool covers, bather loads in spas, and in some states, bather loads in pools.