Ever since I got my first Raspberry Pi I wondered how much power it really requires in my standard configuration, i.e. only with an Ethernet cable and an SD card inserted. Recently I got myself a USB power measurement tool to find out. As you can see in the picture on the left, the Raspberry Pi draws a current of 400 mA with the OS up and running and being idle. With a measured USB voltage of 5.4 V, the resulting power consumption is 2.16 Watts. At an efficiency of 90% of the power adapter itself, the total power consumption is therefore around 2.4 Watts.