What is atomic mass?
Atomic mass is the total mass of protons and neutrons in an atom's nucleus, expressed in atomic mass units (amu) or Daltons (Da). One amu is defined as 1/12 the mass of a carbon-12 atom.
Mass ≈ (Protons × 1.00728) + (Neutrons × 1.00866) amu
1 amu = 1.66054 × 10⁻²⁷ kg
Mass number vs. atomic mass
The mass number (A) is simply protons + neutrons (a whole number). The atomic mass is slightly different due to nuclear binding energy — the "mass defect." This calculator provides both.