I would do this, imagine the next drawing in real life;
Red is worker
brown are the walls
Try to calculate how many workers with the same physical aspect would fit between this space
lets say, 6
Now multiply it for 3 (being blockhead 3 studs large), which would be 18 studs
and then, you could get the length (for example, 3 meters), that would make 18 studs, 3 meters
Of course this is just my thought, it might not be 100% true, but it would work
i think