Why Is a Mole in Chemistry Called a Mole?

Mole Day on calendar
The unit "mole" comes from the word "molecular" and not the furry rodent.

 Ekaterina79, Getty Images

A mole is an important unit in chemistry. Do you know the mole got its name? No, it's not named for the burrowing animal! Here is the answer to why a mole is called a mole.

Key Takeaways: How the Mole Units Got Its Name

  • The mole is a unit used in chemistry that is equal to Avogadro's number. It is the number of carbon atoms in 12 grams of the isotope carbon-12.
  • The word mole comes from the word molecule. It is not related in any way to the animal called the mole.
  • The mole is most often used to convert between numbers of atoms and molecules to the gram mass unit.

Ostwald is responsible for coming up with the term "mole" (Mol), although his original unit was defined in terms of the gram. His later writings made it clear he intended this unit to be based on the ideal gas concept. Around 1900, Ostwald wrote,

"...the molecular weight of a substance, expressed in grams, shall henceforth be called mole [. . . das in Grammen augedruckte [. . .] Molekulargewicht eines Stoffes soll fortan ein Mol heissen]"
"That amount of any gas that occupies a volume of 22414 mL in normal conditions is called one mole [eine solche Menge irgendeines Gases, welche das Volum von 22412 ccm im Normalzustand einnimt nennt man ein Mol]"

Moles even have their own day, aptly named Mole Day.


  • Ostwald, W. Grundriss der allgemeinen Chemie; Leipzig: Engelmann, 1900, p. 11.
    Ostwald, W. Grundriss der allgemeinen Chemie, 5th ed.; Dresden: Steinkopff, 1917, p. 44.
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Helmenstine, Anne Marie, Ph.D. "Why Is a Mole in Chemistry Called a Mole?" ThoughtCo, Aug. 29, 2020, thoughtco.com/mole-in-chemistry-name-meaning-608528. Helmenstine, Anne Marie, Ph.D. (2020, August 29). Why Is a Mole in Chemistry Called a Mole? Retrieved from https://www.thoughtco.com/mole-in-chemistry-name-meaning-608528 Helmenstine, Anne Marie, Ph.D. "Why Is a Mole in Chemistry Called a Mole?" ThoughtCo. https://www.thoughtco.com/mole-in-chemistry-name-meaning-608528 (accessed April 22, 2021).