Per quote from ADG's ADA:
"At about 58 gallons gallons, its trimless construction lends to the impression of a larger tank."
That's the info for the 90-P. For the 75-P, it said:"At about 42 gallons gallons, its trimless construction lends to the impression of a larger tank."
Not sure who's really right, but that's what the official website says. I have a 90-P; maybe I will run the measurement when I set it up