How to judge track size while designing?

I've been testing some track designs, more to get myself comfortable with blender than anything else, but now I wanted to make some of the tracks playable (add relevant objects and scenery). One thing that has always been a problem is size, how do you judge the size of a track or how do you know that a track has enough space for 2 o 3 karts side by side. Do you just create the track and than scale everything up/down to a proper size testing in game?