Hmmm.....another way is to adjust the floor tile, say that every 3 squares is actually a meter, and go from there. Make the cube prop into a ruler that matches the squares....etc. I've been using Lightwave for a short while and even though it will convert between metrics and feet and inches, I've found that the measurements really are mostly practical when building a scene, but the viewer of the final render will have no way of really knowing if everything is to scale anyway, (unless you are designing something like a court re-enactment or something like that.)