Question

How is the atomic mass measured?

Answer 1

You can just plain use the Periodic Table or you can determine by a stable number of protons and neutrons in an atom.

Explanation:

Think, what is the atomic mass of Oxygen?

You can refer to the Periodic Table here: http://www.ptable.com/

You can also know that Oxygen has 8 protons and 8 neutrons, so the atomic mass is 16.

Again, you can refer to the periodic table.

Hope this helped!