Principles for creating WBS

A WBS must be built with sound principles so that it fully and clearly represents the project scope. The basic principles are as follows.

1. 100% rule: the WBS must include 100% of the work defined by the project scope and capture all deliverables, including project management. The sum of the work at the child level must equal 100% of the work of the parent. Nothing outside the WBS is part of the project.
2. Deliverable-oriented: elements should be products, results or services (nouns), not actions only. Example: "Design document" rather than "design".
3. Mutually exclusive elements: no overlap in scope between elements, which avoids duplicated work and cost and ambiguity of responsibility.
4. Hierarchical decomposition: break down level by level from the project down to work packages, and each level is more detailed.
5. Level of detail: decompose until the work package can be reliably estimated, assigned to a person and managed. A rule of thumb is 8-80 hours (the "8/80 rule") or one reporting period.
6. Single responsibility: each work package should be assigned to one responsible unit or person.
7. Appropriate number of levels: usually 3 to 6; too few means vague, too many means micromanagement.
8. Include everything necessary: project management, quality, procurement and training work, not only technical work.
9. Involve the team: people who will do the work should help to create the WBS, which improves accuracy and commitment.
10. Use templates and past WBSs from similar projects.
11. Consistent organisation: choose a clear basis (by phase, product component or function) and apply consistently.
12. WBS dictionary to define each element.
13. Keep updated through change control.
14. Progressive elaboration: later phases can be left at a higher level until more is known (rolling wave planning).

Example: In a software project, "Testing" is divided into Unit test plan, System test report and UAT sign-off, each owned by the QA lead.