The grid filtration area is 48 square feet
And rated at 96 GPM
Edit: according to the owners manual, the flow rate for the pentair fns plus 48, with 48" sqft of filtration, is 120 gpm, based on 2.5 GPM per sqft. Poolcenter.com has it listed at 2.0 GPM per sqft , or 96 GPM.