Planck units

Planck units are a system of units of measurement based on the gravitational constant, Planck's constant, and the speed of light in a vacuum. These units have the advantage of eliminating most of the fundamental physical constants; measured in them, all three constants on which they are based have the value unity. However, they are too small for use for practical purposes, unless prefixed with large powers of ten. They also suffer from uncertainties in the measurement of some of the constants on which they are based.

The SI units are increasingly defined in terms of fundamental constants also, but unlike the Planck units their definition includes arbitrary numbers which are not powers of ten, which are present only for historical reasons.