Answer and explanation;
The atomic mass of a single atom is simply its total mass and is typically expressed in atomic mass units or amu.
Atomic mass is typically calculated by adding the number of protons and neutrons together, ignoring the electrons because of their small size. Protons and neutrons are the larger particles, and are found in the nucleus, which is the core of the atom.
For example; An atom of Carbon has 6 protons and 6 neutrons, it is given an atomic mass of 12 a.m.u which makes each proton and neutron in the nucleus of any element contribute 1 a.m.u to the atom's atomic mass.