The present invention provides a way to more effectively estimate energy usage by devices such as servers, including traditional mainframes as well as other enterprise systems. One core idea surrounds the fact that when detailed power consumption information is unavailable for a specific configuration, power consumption is computed/projected/estimated by de-rating the maximum power rating by a power adjustment factor that would more closely project the true power consumption. Under this approach, the power consumption is then provided as a range specifying probable expected lower and upper limits for a given device. This range is more meaningful for planning and decision-making and shows the client a more likely best and worst case energy consumption scenario for their specific device(s), and hence is helpful for planning or server comparison decisions. Cooling, energy costs, energy efficiency, and energy expanded per MIPS are also projected and given as a range instead of a single number. This gives the IT decision maker more accurate information upon which to base IT decision-making.