The Planck mass is the fundamental unit of mass in the system of Planck units. It has the value:

*m _{P} = 2.18 × 10^{-8}* kg

In SI units, measurements of mass are made in kilograms (usually given the symbol **kg**). While the kilogram is convenient for use in everyday life, such as measuring the mass of a person or the mass of ingredients for a cake, it becomes less practical when we discuss the masses of the elementary particles such as the proton (rest mass of 1.67 × 10^{-27} kg) and the electron (rest mass about 1/1800 that of the proton).

A consequence of using kilograms to measure mass is that the fundamental constants take on values that are not always convenient for including in equations:

Speed of light | c = 299792458 ms^{-1} |

Gravitational constant | G = 6.673(10) x 10^{-11} m^{3} kg^{-1} s^{-2} |

Plank’s constant (reduced) | = h/2π = 1.054571596(82) x 10^{-34} kg m^{2} s^{-1} |

Boltzmann constant | k = 1.3806502(24) x 10^{-23} kg m^{2} s^{-2} K^{-1} |

The Planck mass is derived dimensionally using combinations of these fundamental constants:

By redefining the base units for length, mass and time in terms of the Planck units, the fundamental constants have the values: *c* = *G* = = *k* = 1.

Study Astronomy Online at Swinburne University

All material is © Swinburne University of Technology except where indicated.