Atomic Mass Calculator

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Nuclide mode: atomic mass of one specific nucleus. Average mode: weighted average across natural isotopes.
The atomic number identifies the element (hydrogen = 1, carbon = 6, uranium = 92).
protons
Neutron count. Carbon-12 has 6, Carbon-14 has 8.
neutrons
Atomic mass
12u

Mass of the atom in atomic mass units (1 u = 1 Da)

Mass number (A)12
Mass in kilograms19.9265x 10⁻²⁷ kg
Mass defect0.09894u
Atomic mass (u)12
Mass (x 10^-27 kg)19.9265

C-12: atomic mass ~ 12 u

  • This nuclide has mass number A = 12 (6 protons, 6 neutrons).
  • Standard atomic weight of Carbon on the periodic table is 12.011 u, averaged over all natural isotopes.
  • The mass defect from free nucleon masses is 0.098940 u - this represents energy released as binding energy (E = mc^2).
  • Conventional notation: C-12 (superscript A, subscript Z before the symbol).

Next stepFor the precise tabulated mass of this specific nuclide, look up the AME (Atomic Mass Evaluation) database at IAEA.

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