Determine the total amount of the substance or sample
Determine the amount of the specific isotope, element, or component
Divide the specific amount by the total amount
Multiply the result by 100
Use the formula: percent abundance = (part ÷ total) × 100
If using isotopes, use the average atomic mass and the isotope masses to set up equations
Solve the equations for each isotope’s abundance
Check that all abundances add up to 100%