The size of the pool in need of filtration is the main factor in determining the appropriate size filter. The size of the pump will influence the size of the filter, since the units are oftentimes combined or contained in the same housing. A rule of thumb for pump size, which impacts the filter size, is that all of the pool water should be recycled through the pump and filter within eight hours.

On the Other: Filter Flow Rates

The flow rate of a filter will also impact the size that is appropriate for the pool. Each filter type has a specific flow rate. For in-ground pools, the flow rate of the filter should be higher than the gallons per minute (GPM) of the pump. Calculate the GPM by reviewing the swimming pool calculations in the references section. Above ground pools have pump and filter combination backs, or "skid packs" that are based on the number of gallons the pool contains.

Bottom Line

Selecting the correct size filter is reliant on a few factors--the size/area of the pool, the power of the pump for the pool, the flow rate of the filter and whether the pool is above or in-ground. For in-ground pools, calculate the total gallons in the pool, and then determine the gallons-per-minute that the pump processes. These two calculations will help determine the size of filter needed for a pool. For above ground pools, knowing the total size of the pool will help determine the "skid pack" needed. Skid packs are pre-packaged pump and filter units made especially for above-ground pools.

Source:

Pool Plaza Filter Comparison Chart

Pool Filters

Resource:

Swimming Pool Calculations