Activity resource estimating is a process in which the project team carefully compiles a thorough listing of the resources that will be needed in completing a project. There are six inputs that are to be used in the process of activity resource estimating. Those six inputs are the activity list, the activity attributes, the organizational process assets, the enterprise environmental factors, and project management plan, and the resource availability. There are a number of tools that can also be utilized in most effectively estimating the required activity resources. Those tools include expert judgment, a complete alternatives analysis, the use of published estimating data, project management software, and the use of bottom-up estimating. The resulting outputs from this process include activity resource requirements, activity attributes updates, requested changes, a resource breakdown structure, and the development of a resource calendar. The successful utilization of activity resource estimates will help assure that enough resources are acquired without waste and excessive expenditure.