`rho_"(Universe)" = 3 X 10^-28 (kg)/m^3`

3.0E-28

This equation provides an estimate of the mass desnity of the observable universe.

According to an article posted on the University of Massachusetts website  ¹ , "the mass density of visible matter (i.e., galaxies) in the Universe is estimated at `3 X 10^-28 "kg"/m^3`.

1. ^ Mass, Size and Density of the Universe