Depends on the model.
'72 Center Console is excellent self bailing.
Last month had a fish hooked, and ran too fast in reverse too long, which placed water about 5+" deep in back while running backwards. Only needs about 6" to be under water! Went forward just in time, kept bow up at speed, and about 3 minutes later, she was dry. Later on at ramp, pulled drain plug, and dry as a bone.
Couple months ago converted to the ping pong ball looking scuppers. Highly recommend.
Under normal usage, I would guess that with the new scuppers, never more than 1/2 cup of water in rear of boat when sitting still. Previous flappers always left an inch of water (or more) back there. Still, never had any water go into bilge.
This old boat never had a bilge pump in it! I guess if it has enough water to need a bilge pump, it's probably sunk already anyway..