A new approach for the determination of activation energy and attempt frequency for the diffusion of single adatoms on a surface is proposed and demonstrated for Pt adatom diffusion on Pt(111). The method is based on a combination of low temperature scanning tunneling microscopy (STM) measurements and kinetic Monte Carlo simulations. The method involves only a minimum of assumptions and is independent of classical nucleation theory. This independence allows one to analyze the applicability of the latter. In addition, it is found that the measurement of the mean square displacement of individual adatoms is influenced by the STM tip.