SI Units – Amount of Substance

One mole (mol) contains exactly 6.02214076 × 10²³ elementary entities. This number is the fixed numerical value of the Avogadro constant, N_A, 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

Credit: photo: R. Press/NIST; graphic design: N. Hanacek/NIST

• SI Base Units Relationship Poster (SP 1247) (NIST) – a colorful poster illustrating the relationships of the International System of Units (SI) derived units with special names and symbols and the seven traditional base units. 
• SI Units Card Deck (SP 1297) (NIST) – this activity offers a fun way to enhance understanding of the International System of Units, including the defining constants, base units, derived units with special names, and prefixes.
• Redefining the Mole (NIST)
• National Mole Day – Celebrated annually on October 23 from 6:02 a.m. to 6:02 p.m. to commemorate Avogadro's Number (6.02 x 10²³). (National Mole Day Foundation)
• Mole Day (American Chemical Society)
• Mole Day – Avogadro & the Mole (Compound Interest)
• The Mole – Practice mole calculations. (Jason Learning)
• Introduction to the Mole (Pennsylvania Department of Education)
• How Big is a mole (TedEd)
• Amedeo Avogadro (Science History Institute)
• Introducing High School Students to the Avogadro Number and the Mole Concept Using Discovery with Calculations Based on Physical Properties of Elements, Crystal Structures, and 28Si Spheres, Journal of Chemical Education, 98, 3, 790-795. T. H. Bindel. (January 29, 2021) – DOI: 10.1021/acs.jchemed.0c01132.  Explore an instructional approach where students discover the Avogadro number and the mole concept.
• Top 10 Tips for Teaching the Metric System (NIST)

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Credit: J. Wang and B. Hayes/NIST ©2020 U.S. Secretary of Commerce. All Rights Reserved.

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

• SI Units
• Fundamental Physical Constants
• Length – meter (m)
• Time – second (s)
• Electric current – ampere (A)
• Temperature – kelvin (K)
• Luminous intensity – candela (cd)
• Mass – kilogram (kg)

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