Reducing the energy footprint of digital devices and software is a task challenging the research in Green IT. Researches have proposed approaches for energy management, ranging from reducing usage of software and hardware, compilators optimization, to server consolidation and software migration. However, optimizing the energy consumption requires knowledge of that said consumption. In particular, measuring the energy consumption of hardware and software is an important requirement for efficient energy strategies. In this review, we outline the different categories of approaches in energy measurements, and provide insights into example of each category. We draw recommendations from our review on requirements on how to efficiently measure energy consumption of devices and software.