We'll learn how to use moles to figure out how many atoms you have in something. If there are 602 hexillion things in a mole, how do you count them all? By using the periodic table, you can figure out the molar mass, the amount that one mole of a substance weighs. Once you weigh something to determine how many moles are in it by using molar mass, Avogadro's number allows you to figure out how out how many atoms there are.