This paper presents a multi-layer power and energy estimation approach for embedded applications and operating systems. The multi-layer methodology is an incremental approach where we consider that energy can be summed over the hyper period of the real-time system. At the first layer, we start by estimating energy and power consumption of standalone tasks. At the following layers, we add energy overheads of embedded operating system services such as timer interrupt, inter process communications (IPC)) and peripheral devices accesses.\\ We illustrate our Multi-layer approach by estimating the energy consumption of an M-JPEG encoder running on linux 2.6 and deployed on a XUP Virtex-II pro development board.