The battlefield consists of tiles which measure 40*40 meters.
Two and a half tiles are 100 meters.
It's not that easy to see the individual tiles, depends on the map. There's also a map in one of the mappacks that only shows a grid and makes measuring easy.

Yuuki may correct me here, but I think that a 60 men unit in 3 ranks has a width of one texture tile (40 meters).