Joulemeter is a software based mechanism to measure the energy usage of virtual machines (VMs), servers, desktops, laptops, and even individual softwares running on a computer. Joulemeter estimates the energy usage of a VM, computer, or software by measuring the hardware resources (CPU, disk, memory, screen etc) being used and converting the resource usage to actual power usage based on automatically learned realistic power models. Joulemeter can be used for gaining visibility into energy use and for making several power management and provisioning decisions in data centers, client computing, and software design.