##### SI defining constant
Name Symbol Value Unit Expressed in terms of SI base units
Avogadro constant NA 6.022 140 76 × 1023 mol−1 mol−1

### Definition

The numerical value of the Avogadro constant, symbol NA, is defined to be exactly 6.022 140 76 × 1023 when expressed in the unit reciprocal mole, symbol mol−1.

The Avogadro constant, NA, forms the basis for the definition of the mole.

### Nature

The Avogadro constant NA is a proportionality constant between the quantity amount of substance (with unit mole) and the quantity for counting entities (with unit one, symbol 1). Thus it has the character of a constant of proportionality similar to the Boltzmann constant k.