Value of N_{A} in various units 

6.02214179(30)×10^{23} mol^{−1} 
2.73159757(14)×10^{26} lbmol^{−1} 
1.707248479(85)×10^{25} ozmol^{−1} 
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)×10^{23} mol^{−1}. The constant was named after the Italian scientist Amedeo Avogadro.
The measurement of Avogadro's constant was refined in 2011 to 6.02214078×10^{23} ± 1.8E7×10^{23}.
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 carbon12. Avogadro's number is a dimensionless quantity and has the numerical value of the Avogadro constant given in base units.
Related pages
Images for kids

Ballandstick model of the unit cell of silicon. Xray diffraction measures the cell parameter, a, which is used to calculate a value for Avogadro's constant.