 In chemistry and physics , the Avogadro constant ( named after the scientist Amedeo Avogadro ) is the number of constituent particles , usually atoms or molecules , that are contained in the amount of substance given by one mole . Thus , it is the proportionality factor that relates the molar mass of a compound to the mass of a sample . Avogadro 's constant , often designated with the symbol NA or L , has the value 6 @.@ <unk> ( 74 ) × 1023 mol − 1 in the International System of Units ( SI ) . 
