Value of N_{A} in various units 

14179(30)×10^{23} mol^{−1} 6.022 
59757(14)×10^{26} lbmol^{−1} 2.731 
248479(85)×10^{25} ozmol^{−1} 1.707 
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 14129(27)×10^{23} mol^{−1}. The constant was named after the 6.022Italian scientist Amedeo Avogadro.
The measurement of Avogadro's constant was refined in 2011 to ×10^{23} ± 6.02214078×10^{23}. 0.00000018
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.
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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.