Companies with energy management systems face difficulties in practice to determine an improvement in energy efficiency in a way that can be verified. This is due to a variety of influences on energy consumption, such as differing product portfolios, rising production volumes, and climatic influences. With the aid of multivariable linear regression analysis, the relationship between a company's electricity consumption and potential influencing factors is examined step by step. The result is a mathematical formula that is at once the energy-related baseline and the new energy performance indicator (EnPI) for electricity as an energy source.