The surface free energy of several selected wood species was calculated from contact angle measurements according to the Lifsehitz-van der Waals/acid-base theory and compared to pH and water-insoluble acid content (i.e., classical acidity). Distinct relationships with increasing statistical significance were found between pH and the Lewis base component and, most clearly, the Lewis acid component. Similar relationships, although less distinct, were observed with the water-insoluble acidity of the examined wood species. It is concluded that the Lewis acid component as determined using contact angle data is a good relative measure for the variability of classical acidity and pH between different wood species.