In physics, the Planck mass is the unit of mass in the system of natural units known as Planck units. It is defined using: c, the speed of light in a vacuum; G, the gravitational constant; and the Planck constant over 2Pi.
The unit is named after Max Planck. The unit measures the approximate scale at which quantum effects, in the case of gravity, become important. This constant is expressed in units of kilograms.
This constant, the Planck Mass, mP, is specified with the standard uncertainty (standard deviation) of 0.00013 x 10-8 kg
See Uncertainty of Measurement Results, a discussion provided by NIST of the application of uncertainty to the documented constants.