About 3000-4000 grams. A 28qt has the same footprint as a 32qt. They are just about an inch less in height. People will argue about 28-32qt being too small for big girls, but I'll say otherwise. I've bred and produced many in them, and some females just stop feeding when moved into bigger tubs.
I say 3000-4000 because I have a het pied girl that tops my scale out and she's been in a 28-32 her whole life.....she's probably closer to 5k. Most of my others are in the 2000-3000 gram range. Personal preference.