What is the 100% rule in WBS?

The 100% rule in the Work Breakdown Structure (WBS) means that all work for the project must be fully reflected in the WBS — no task or work element should be omitted or duplicated.

This rule ensures that:

• All work necessary to complete the project is included.
• There are no unnecessary or unrelated elements.
• The sum of work at all levels of the WBS equals 100% of the project scope.

Thus, the 100% rule helps ensure completeness and accuracy of planning, and also serves as a basis for estimating time, cost, and resources for the project.