In chemistry, a mole is a unit of measurement used to express the amount of a chemical substance. It is defined as the amount of a substance that contains as many elementary entities, such as atoms, molecules, ions, electrons, or photons, as there are atoms in 12 grams of carbon-12. The mole is an extremely large number, 6.02214076 × 10^23, and is also known as Avogadros number or Avogadros constant. The mole is used to measure large quantities of very small entities, such as atoms, molecules, or other specified particles. The concept of the mole helps to put quantitative information about what happens in a chemical equation on a macroscopic level. The mole is one of the base units of the International System of Units (SI) and has the unit symbol mol/10%3A_The_Mole). The mole is used to convert between mass and number of particles, and the mass of one mole of a substance is called its molar mass.