**Encyclopaedia Britannica states that there are 602,000,000,000,000,000,000,000, or 602 followed by 21 zeroes, atoms in a mole.** This number is read aloud as "602 sextillion" and is a reference to Avogadro's number, which is commonly expressed in scientific notation as 6.02 multiplied by 10 to the 23rd power.

A mole contains the same number of units by definition, which is regardless of the substance. A mole is also related to atomic weight or mass. For example, one mole of carbon-12 atoms has an atomic weight of 12 grams, while a mole of oxygen, which also contains Avogadro's number of units, has an atomic weight of 16 grams.