Advances in window technologies and the desire to standardize the reporting of standardswindow heat transfer indices have necessitated the development of a comprehensivesanalytical procedure for calculating heat transfer through windows. This paper showsshow complete window heat transfer can be considered as the area-weighted sum of thesthree window component areas: the center-of-glass area, the edge-of-glass area, and thesframe area. Algorithms for calculating heat transfer through each of these areas and forscombining these to calculate total window indices are presented.