level 3 it is 6k
level 4 it is 11.5k
level 5 is 19k
level 6 is 28.5k

I can only base this information on previous seasons but this is the maximum capacity you can achieve on your level.

No matter what size stadium you build, you can never achieve more than the stated capacity ABOVE

Obviously set ticket prices to max out your stadium capacity and get the full 5% bonus in game.

Anybody who can verify stadium capacity limits at higher levels please add, and I will edit this post accordingly.

I am looking for maximum ground capacity at any given level