Size is weird in Zero-K, trees are a thing and they suggest the robots are about building-sized, which is weird to begin with since it means even the likes of fleas are the size of cars or so.
But then there are things like that that imply the maps are entire continents or so.
The entire family of TA-like games seems equally confused regarding how big these robots are supposed to be.
I suppose we can assume the trees are huge and everything is city-sized instead.