Planck Density

The Planck density is the unit of density, denoted by $\rho_P$, in the system of natural units known as Planck units. $1\ \rho_P \ is \approx 5.155 \times 10^{96} kg/m^3$. This is a unit which is very large, about equivalent to $10^{23}$ solar masses squeezed into the space of a single atomic nucleus. At one unit of Planck time after the Big Bang, the mass density of the universe is thought to have been approximately one unit of Planck density.