The hydraulic loading is one of the factors
which will influence the performance of filters. It is
defined as the amount of wastewater applied per day over the
surface area of the media. So its units are gallons/day/square
foot.

The following formula can be used to calculate the hydraulic
loading of a filter, including recirculation:

Given a total flow of 3 mgd and a filter area of 7,850
ft^{2}, the hydraulic loading would be:

So the hydraulic loading is 382 gpd/ft^{2}.