It’s a tricky question- how do you quantify the size of a diaper?
There are endless variables to be controlled- or simply ignored. Do you measure it when it is new and dry? Do you measure it at max capacity- and if so, how do you define maximum capacity?
Mass seems like the best measurement, but it’s really not easy to measure.
Weight is interesting, but really only describes how much piss you managed to absorb into the diaper.
I decided length is the easiest metric to use.
It gets complicated to decide where the diaper begins & ends, so I measure from the small of my back (the spot where my fingertips naturally land between my shoulder blades), to the top of my sternum. This way I get a rough number describing the bulk of a diaper, and avoid having to define exactly where the diaper begins & ends.
This measurement does have it’s faults for sure. Bulk in the front and back will have less effect on the length than bulk in the crotch. And a loose or sagging diaper will measure as larger than a well-worn tight diaper. Finally, bulk on the sides (which for me is part of what makes a really good ridiculously-thick diaper) is ignored.