The design of the data center is dependent on the balance of two sets of capacities:
Data center capacities: Power, cooling, physical space, weight load, bandwidth (or connectivity), and functional capacities
Equipment capacities: The various devices (typically equipment in racks) that could populate the data center in various numbers
Depending on the chosen site of the data center, one of these sets of capacities will usually determine the other. For example, if the project scope includes a preferred amount of equipment capacity for the data center, the knowledge of the equipment requirements can be used to determine the size of the center, the amount of power and cooling needed, the weight load rating of the raised floor, ...