Avogadro's constant

See for more details Avogadro's number.

The SI definition of Avogadro's constant (designated N_A) is: the number of entities (such as atoms, ions, or molecules) per mole. (This definition requires a definition of mole that does not rely on N_A, but one that is in terms of ¹²C atoms). The constant N_A has dimension mol⁻¹. The numeric value of Avogadro's constant is N_A = 6.022 140 76 x 10²³ mol⁻¹.

Reference:

https://www.nist.gov/si-redefinition/meet-constants