To calculate the GPM capacity of a floor drain, I found the following equation:
Q = 448.2 Cd A 2gh where Q = Flow Rate (Gallons per Minute)
Cd = Discharge Coefficient (Typically 0.6)
A = Open Area of Grate (ft2)
g = Acceleration (32.2 ft/s2)
h = Head Above the Floor (ft)
What is meant by head above the floor for h? the floor drain is flush with the floor.