The Planck density is the unit of density, denoted by ρP, in the system of natural units known as Planck units.
- ≈ 5.1 × 1096 kg/m3
- mP is the Planck mass
- lP is the Planck length
- c is the speed of light in a vacuum
- is the reduced Planck constant
- G is the gravitational constant
This is a unit which is very large, about equivalent to 1023 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.