How I caculated it was I looked at Battlemechs. When you move, it shows this display:
As you can see, the mechs walk an average of about 50 feet per space. Assuming this translates to Supermechs, one distance of walking is equivalent to ~50 feet. I’m confident that this translates as in Battlemechs, the mechs take more time to move, wheras now, our mechs are larger and take less time to move.
If you want to know a mech’s height, flip one space on its side and you’ll find the height is pretty much equal. Thus, I’ve concluded that the standard arena is ~450 feet long, and the average mech is ~50 feet long.
This information is subject to change, and you can always develop your own theories, this is just mine.