Between 2000 and 2006, energy requirements for data centers doubled, and they are on track to double again by 2011. In the same time period, typical per-rack heat densities went from 1 kW to 7 kW, and they are estimated to exceed 20 kW per rack by 2010. This places tremendous importance on a data center facility planners ability to properly budget for future power and cooling infrastructure requirements. In the past, facilities planners used IT equipment nameplate ratings values as a method to plan power and cooling capacity requirements, which resulted in over-built, under-utilized, inefficient infrastructure. Todays energy costs and efficiency demands necessitate a more accurate method of determining those requirements. This white paper has been developed to introduce the reader to the many new and highly accurate software tools available for estimating power and cooling capacity requirements.