It's been a while (nearly 3 months) since we had something statistic-y, so here's a chart I made by hand (excel), mostly to satisfy my own curiosity.

It's sorted by largest number of estates first. And for the Grand Fate (because they average about 1 noble per square league) that reads 139 nobles, 140 square leagues. Yes, Size = Square Leagues, rounded to the nearest full league.

If you're interested, I'm thinking about posting a breakdown of some of the largest realm's sub-realms as well, but not sure which realms to include. I can also do one for baseline commoner population as well (as I gathered those numbers at the same time as this).