What constant is exactly 6.02214076×10^23 per mole?

The constant exactly equal to 6.02214076×10^23 per mole is the Avogadro constant.

It connects the amount of a substance to the number of specified entities—such as atoms, molecules, ions, or electrons—in a sample. One mole contains exactly 6.02214076×10^23 entities, making the value exact rather than experimentally approximate.

The constant is named after Italian scientist Amedeo Avogadro, whose 1811 hypothesis linked gas volume with the number of particles present. The term “Avogadro number” is often used for the numerical value, while “Avogadro constant” properly emphasizes the quantity expressed per mole.

A common mix-up is confusing it with the gas constant, R, which relates pressure, volume, temperature, and amount in gas laws. The 2019 SI revision fixed the Avogadro constant exactly and used it to redefine the mole.