Hey Chris,

The sizes of the current Middleweights vary a fair bit. Jibril 1.6 was about 700mm long, ~540mm wide and ~350mm high but robots like Backflip and Jackpot are significantly longer and taller/wider and lower respectively. Raphael is about a metre wide and pretty high off the ground.

I would probably say 700mm wide is "not bad" as a starting point.