Mole (mol)

ScientificCurrent unit

Exactly 6.02214076×10²³ entities (the Avogadro number). The SI unit for amount of substance in chemistry.

1 mole = 6.02214076×10²³ pieces (exactly).

About the mole

The mole counts particles the way a dozen counts eggs, only on a vastly larger scale: exactly 6.02214076 × 10²³ elementary entities, which may be atoms, molecules, ions, electrons, or other specified particles. The mole became the seventh SI base unit in 1971, and the term itself dates from around 1900, shortened from the German Molekül. In 1909 Jean Perrin named the number in honor of Amedeo Avogadro.

Until 2019 a mole was the number of atoms in 0.012 kilogram of carbon-12, so the count depended on the kilogram. Effective May 20, 2019, the SI fixed the number itself, and the mole no longer rests on a physical sample. As a result the molar mass of carbon-12 is no longer known exactly. The chosen number kept it at 0.012 kilogram per mole, with a relative uncertainty of 4.5 × 10⁻¹⁰, at the moment of adoption. For scale, about 18 grams of water holds roughly this many molecules.

Sources: BIPM SI Brochure, 9th edition (2019); NIST: Redefining the mole; Wikipedia: Avogadro constant

Mole conversion chart

1 mole expressed in every other counting & quantity unit:

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