With SimArena you can calculate the optimal size of your arena for the online manager game Hattrick depending on the amount of fans you have. Just login with your username and security code and you'll get the best distribution and optimal size for your arena. Values like Profit/Week, Break even and NPV (Net Present Value) are calculated and will make you the decision of resizing your arena more simpler.
The currently used distribution is 65.3% for Terraces , 24.2% for basic seating , 8.4% seats under roof and 2.2% seats in VIP boxes.
If you are interested in more statistics for the arena, you'll find more statistics here.