Find each isotope of the element
Note the mass of each isotope
Note the natural abundance of each isotope
Convert each abundance percentage to a decimal
Multiply each isotope’s mass by its decimal abundance
Add all the products together
Use this formula: atomic mass = (m1 × a1) + (m2 × a2) + (m3 × a3) + …
Express the final value in atomic mass units (amu) or daltons