 Accurate determinations of Avogadro 's number require the measurement of a single quantity on both the atomic and macroscopic scales using the same unit of measurement . This became possible for the first time when American physicist Robert Millikan measured the charge on an electron in 1910 . The electric charge per mole of electrons is a constant called the Faraday constant and had been known since 1834 when Michael Faraday published his works on electrolysis . By dividing the charge on a mole of electrons by the charge on a single electron the value of Avogadro 's number is obtained . Since 1910 , newer calculations have more accurately determined the values for the Faraday constant and the elementary charge . ( See below ) 
