ELI5: Explain Like I'm 5

Planck mass

Planck mass is a very small mass that scientists have named after a famous scientist named Max Planck. It is equal to about 2.17 x 10^-8 kilograms, which means it is an extremely tiny amount of mass. Planck mass is so small that it is the approximate mass of a single atom. It is about 10 billion times smaller than the mass of a single grain of sand!