The dalton or unified atomic mass unit (abbreviated: amu, u, or Da) is a unit of measurement that is used to measure the mass of atoms. The atomic mass unit is equal to one twelfth of the mass of the carbon-12.
The unified atomic mass unit and the dalton are different names for the same thing. The word 'dalton' is being used more over time.[1][2][3] The unit is named after John Dalton, an 18th-century naturalist and teacher.