Orders of magnitude (mass)

The kilogram is the only standard unit to include an SI prefix (kilo-) as part of its name.

However, the names of all SI mass units are based on gram, rather than on kilogram; thus 103 kg is a megagram (106 g), not a *kilokilogram.

The tonne (t) is an SI-compatible unit of mass equal to a megagram (Mg), or 103 kg.

For subatomic particles, physicists use the mass equivalent to the energy represented by an electronvolt (eV).

Planck's law allows for the existence of photons with arbitrarily low energies.