avogadro's number calculating number of atoms
D=Density, V=Volume. Amadeo Avagadro proposed, in 1811, that equal volumes of gas contains an equal number of atoms or molecules, if the two volumes are held at the same temperature and pressure. This proposal became the Avagadro's Hypothesis. Actually, Avogadro's number (N) refers to the number of molecules in one gram-molecule of oxygen.