An atomic unit of mass is defined as accurately 1/12 the mass of a carbon-12 atom. The carbon-12 atom has six neutrons and six protons in its nucleus. The atomic unit mass is symbolized as AMU or amu.
1 AMU = Average of the proton rest mass and the neutron rest mass.
1 AMU = 1.67377 x 10 -27 kilogram or 1.67377 x 10 -24 gram.