A method, system, and computer program product for selecting a transformer size for an industrial or commercial facility. A plurality of end-use connected load data for the facility is entered via a user interface into a memory of a computing system for determining facility load diversities. A base homogeneity is determined for the end-use connected load data. An initial facility diversity is determined based on the end-use connected loads and initial end-use diversities. A total facility diversity is determined based on the initial facility diversity, the base homogeneity, and a total connected load. An expected energy demand is determined based on the total facility diversity and a total connected load. The end-use diversity is adjusted for at least one end-use and a change in expected energy demand for the facility is allocated to each end-use. The transformer size is determined for a total expected energy demand and a total hours use for each connected load.