According to the PMBOK® Guide, specifically within the Estimate Costs process, Activity Cost Estimates are the quantitative assessments of the probable costs required to complete project work.
Nature of the Estimate: These estimates include the costs for all resources that will be charged to the project. This includes, but is not limited to, direct labor, materials, equipment, services, facilities, information technology, and special categories such as an inflation allowance or a contingency reserve.
Granularity: Cost estimates are developed for each activity identified in the project. These individual activity estimates are then aggregated to develop the Cost Baseline and the overall project budget.
Goal: The ultimate purpose of generating these estimates is to determine the amount of funding required to physically execute the activities and produce the deliverables as defined in the project scope.
Analysis of Other Options:
A. Create WBS: This is a planning process that occurs before cost estimation. While the WBS provides the framework for estimating, the estimates themselves are not " required to create " the WBS; rather, the WBS is required to create the estimates.
C. calculate costs: This is redundant. While you do calculate costs to get the estimates, the PMBOK® definition specifically links the purpose of the quantitative assessment to the completion of the actual work/activities.
D. Develop Project Management Plan: While activity cost estimates are eventually integrated into the Project Management Plan (as part of the Cost Management Plan or Cost Baseline), they are specific to the execution of work, not the act of writing the management plan itself.
