In the field of information and computer technology (ICT), saving energy has its focus set on energy efficient hardware and its operation. Recently, efforts have also been made in the area of computer software. However, the development of energy efficient software requires metrics, which measure the software's energy consumption as well as models to monitor and minimize it. In software and software development processes they hardly exist. In this work we present a generic metric to measure software and a method to apply it in a software engineering process.