Skip to main content
U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

SI Units – Amount of Substance

SI Units mole banner
Credit: NIST
mol - Mole - Amount of Substance - 2018

One mole (mol) contains exactly 6.02214076 × 1023 elementary entities. This number is the fixed numerical value of the Avogadro constant, NA, when expressed in the unit mol−1 and is called the Avogadro number. The amount of substance, symbol n, of a system is a measure of the number of specified elementary entities. An elementary entity may be an atom, a molecule, an ion, an electron, any other particle or specified group of particles.

When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles, or specified groups of such particles.

The SI unit of concentration (of amount of substance) is the mole per cubic meter (mol/m3).

Resources for Students and Teachers

three metal cubes: aluminum, copper and carbon. Next to the cubes is a quarter to show relative size and mass. All three are one mole's worth of atoms.
Credit: photo: R. Press/NIST; graphic design: N. Hanacek/NIST
graphic image of SI Superhero, The Mole
Credit: J. Wang and B. Hayes/NIST

League of SI Superheroes – The Mole

This comic book-style video animation series has been developed to help middle school students learn about the 7 SI base measurement units. Able to sniff out and count the atoms of every element, the Mole is the king of chemistry. Equal to about 600 sextillion (that's a 6 followed by 23 zeros!), a mole is a shorthand way to talk about huge numbers, especially of tiny things.

Navigate to more SI base unit information:



Created June 21, 2011, Updated January 16, 2024