Atomic mass constant

In physics, the atomic mass constant mu is 1/12 of the mass of the 12C nuclide, in its ground state and at rest.

m_\mathrm{u} = \frac{1}{12}m(^{12}C). $$ By definition  mu is equal to 1 u, the unified atomic mass unit. The latest value is mu = 1.660&thinsp;538&thinsp;921 &times; 10&minus;27 kg.