You'll need more than a ruler.

As humans have evolved their perception of the universe has changed. Originally life had no concepts or thoughts of any kind. This progressed into an awareness of self, that others exist, that they live in a place (their immediate surroundings), that others have thought, that they live in a large place, that there's a lot of others, that there are whole new masses of land and new people, that there's lots of unimaginably small things and unimaginably large things, that people that live in other places are as complex. . . Well you're still working on that one but you'll get there. If you followed life and expressed it to its greatest extent where nothing in all of space and time was beyond its comprehension. Where you ended up. That's how big my dick is.