Many researchers and lecturers have reported that the concept of the mole and Avogadro's number are frequently misunderstood by first-year science students. For this reason, it is highly recommended to introduce this fundamental number to high school and freshman science students as clearly as possible. Therefore, it is pedagogically very useful to diversify the methods of determination of Avogadro's number which are based on basic physics phenomena accessible to those classes of students. Along these lines, I will describe here an unusual method based on the classical Hall effect for determining Avogadro's number. The present method is not relevant for its accuracy but mainly for its simplicity and its "cleanness" compared to the usual electrochemical method used at this instruction level. In addition, this method provides an extra useful test for the validity of the free electron model.