This table shows settling chamber surface area.
Link to this table

Sand Filter Maximum Ponding Depth (feet)
<4
4 to 10
Impervious ≥75% (0.25*Vwq)/Dmax (0.25*Vwq)/Dmax
<75% (0.25*Vwq)/Dmax 0.066*Vwq
Perimeter Sand Filter Maximum Ponding Depth (feet)
<7.5 8 to 10
Impervious ≥75% (0.5*Vwq)/Dmax (0.5*Vwq)/Dmax
<75% (0.25*Vwq)/Dmax 0.066*Vwq