Simple modifications of Trouton’s rule for estimating the entropy of boiling of organic compounds are presented. An empirical equation is developed which expresses the entropy of boiling as a function of molecular flexibility and hydrogen bonding. This equation, which enables the simple yet reasonable estimate of entropy of boiling directly from molecular structure, was generated from a training set of 850 structurally diverse compounds. The average absolute percent error for a test set of 88 compounds is 2.5% which is more accurate than Trouton’s rule.