# Avogadro's constant

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*13 January 2011*.*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 ^{12}C atoms). The constant *N*_{A} has dimension mol^{−1}.
The numeric value of Avogadro's constant is *N*_{A} = 6.022 141 79 x 10^{23} mol^{−1}.

Because the mole and Avogadro's number are defined in terms of the atomic mass constant (one twelfth of the mass of a ^{12}C atom), Avogadro's *constant* and *number* have by definition the same numerical value. In practice the two terms are used interchangeably.

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