Avogadro constant

The Avogadro constant (symbols: L, N_A) is the number of particles (usually atoms or molecules) in one mole of a given substance. Its value is equal to 6.02214129(27)×10²³ mol⁻¹. The constant was named after the Italian scientist Amedeo Avogadro.

The measurement of Avogadro's constant was refined in 2011 to 6.02214078×10²³ ± 0.00000018×10²³.

An old term closely related to the Avogadro constant is Avogadro's number. Avogadro's number is the number of atoms in 12 grams of the carbon isotope carbon-12. Avogadro's number is a dimensionless quantity and has the numerical value of the Avogadro constant given in base units.