The Planck density is the unit of density, denoted by dP, in the system of natural units known as Planck units. It is defined as:
- ≈ 3.26456 × 1094 kg/m3 (Lorentz–Heaviside version)
or
- ≈ 5.15518 × 1096 kg/m3 (Gaussian version)
where:
- mP is the Planck mass
- lP is the Planck length
- c is the speed of light in 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.
The Planck density is thought to be the upper limit of density.