Energy efficiency is a vital characteristic of any mobile application, and indeed it is becoming an important factor for user satisfaction. For this reason, in the recent years several approaches and tools for measuring the energy consumption of mobile devices have been proposed. Hardware-based solutions are highly precise, but at the same time they require costly hardware toolkits. Model-based techniques require a possibly difficult calibration of the parameters needed to correctly create a model on a specific hardware device. Finally, software-based solutions are easier to use, but they are possibly less precise than hardware-based solution. In this demo, we present PETrA, a novel software based tool for measuring the energy consumption of Android apps. We also provide evidence that our tool is able to perform similarly to hardware-based solutions.