What is the origin of Avogadro's number and how is it determined?

Avogadro's number is named after Italian scientist Amedeo Avogadro, who proposed in 1811 that equal volumes of gases at the same temperature and pressure contain the same number of molecules. Avogadro's number is determined experimentally by measuring the mass of a known number of atoms or molecules and then calculating the number of particles in a mole based on this mass.