An atomic mass unit is defined exactly as

Atomic mass is the mass of an atom in atomic mass units (amu)

Atomic mass

• atomic mass (sometimes called atomic weight) is the mass of the atom in atomic mass units (amu). (from periodic table)

o One atomic mass unit is defined as a mass exactly equal to one-twelfth the mass of one carbon-12 atom. Carbon-12 is the carbon isotope that has six protons and six neutrons. Setting the atomic mass of carbon-12 at 12 amu provides the standard for measuring the atomic mass of the other elements.

o For example, experiments have shown that, on average, a hydrogen atom