Relative Atomic Mass

This is the weighted mean of all the naturally occurring isotopes of an element, relative to 1/12 of the mass of carbon 12.

The mass number is equal to the number of protons and neutrons in the nucleus of a particular atom. Remember that protons and neutrons make up almost all of the mass of an atom. The relative mass of an electron is approximately 1/2000 of that of a proton or neutron and so the mass that they contribute is negligible.

What is the actual mass of a proton?