Atomic mass unit

The unified atomic mass unit (u), or dalton (Da), is a small unit of mass used to express carbon-12 nuclide, at rest and in its ground state.

1 u = 1/N_A Avogadro's number)

1 u ≈ 1.660538782(83) × 10⁻²⁷ kg ≈ 931.494028(23) MeV/c²