Some of it is based on height.
Hall tall is the tank?
How tall is the bowl?
I find that anything over 500 grams works well.
In my last house I installed two Toto Carlyle's - Sanagloss models, and well worth it. Great toilets, but they are rated 625 grams on Terry's site. The Ultramax (two in my new house, thanks to the previous owner), is rated at 700 grams, and the Drake rates at 900 grams. Why does the Aquia, which isn't even G-max, rate at 800 grams, higher than some of the 'commercial-grade' G-maxes?
If all G-max are 3" flush valve, 2 1/8" fully-glazed computer-designed trap, then why the variation? I'm not looking to push them to their limits, but I've always wondered about this.
thanks Terry - for the reply, and for everything I've learned from your site over the past few years.
Makes sense - tank and bowl height would influence pressure head independant of flush valve size. I agree completely about the anything over 500 grams as well.
If you look at the MaP report most of the 1 pc. toilets fall into that slightly lower performance for that one reason. Height of the water in the tank.