To me it depends how the animal does, I have moved 500 grams females in 41 quarts tubs but I have also kept 1000 grams ones in 15 quarts tubs, those are not the norm it's based on individual behavior, generally speaking girls 1500 grams and over go in 41 quarts tubs.
Also depends on the rack itself, open or enclosed rack etc.
As for males I have 2 males right now that are in the 750 / 850 grams range and they are in 15 quarts tubs while all the other some with similar size are in 32 quarts tubs.
15 quarts and 32 quarts sterilite tubs used for animal plastic racks can be found at Target.