The equation for the optical absorption coefficient alpha in terms of the average measured reflection and transmission coefficients r and T is derived. A set of tables of alpha d, where d is the sample thickness, as a function of T in intervals of 0.2% for parameters of r in 0.5% is included. Both r and T values range between 0 and 100 %. In addition, tables for the bulk reflectivity R as a function of r and T are given. (Author).