What is approximate density of our universe?

Answer 1

About 1 atom per cubic meter. I assume that would be hydrogen atom. That comes to about 1.67 × 10^-27 kilograms per cubic meter. It's only known to within a fact or a few, however.

Incidentally, I just dug a one cubic meter hole today to plant a peach tree. It took the whole day. I can assure you, that's a lot of space for one atom to hang out in.