What is a work breakdown structure?
A work breakdown structure (WBS) is a project management tool used to define and manage a project's deliverables. The WBS is a hierarchical structure that breaks down complex activities into smaller deliverables (often called work packages, tasks, sub-tasks, or terminal elements), making the work easier to evaluate, assign, and track while also showing how the pieces relate to one another.
While most project management tools focus on planned actions, a WBS focuses on planned outcomes. A carefully organized work breakdown structure can help a project manager more effectively oversee the completion of otherwise complicated tasks within a project. A WBS with measurable, clearly defined tasks can also help project management assign accurate costs and deadlines to a project, simplifying project planning and monitoring.
Elements of a good work breakdown structure
When constructed thoughtfully, a WBS can make it easy to assign and track various elements in a project. In order to maximize its effectiveness, a work breakdown structure should exhibit the following attributes:
- Defined: Your WBS should be easily understood by project participants and stakeholders.
Easily estimated: Task durations, cost, and required resources are included to estimate the cost and time necessary to complete the project.
- Manageable: To reinforce accountability, ensure each work package has a clear owner (a specific team or individual) and can be completed within a reporting period.
Measurable: A WBS should include start and completion dates and assessable milestones to accurately measure progress.
- Flexible: Your structure should accommodate minor changes, such as deadline shifts or the addition of tasks. However, keep in mind that one purpose of the work breakdown structure is to give a full picture of the deliverables expected beforehand to avoid scope creep or rework.
Follow these guidelines to ensure that your work breakdown structure is an effective project management tool:
- Get granular. Break down your project deliverables to their lowest level possible, and express the task in verb form. As a practical benchmark, many teams apply the "8/80 rule," keeping each work package sized to roughly 8–80 hours of effort (or no more than about 10 days or a standard reporting period, depending on your organization).
- Check your WBS for accuracy. Ensure that all of your deliverables, deadlines, and resources are correctly recorded in your visual.
- Include supporting activities. Make sure your WBS accounts for activities such as training and testing, as well as product or service launches and implementation. Include non-IT and procedural work activities, such as documentation and reviews, in your work structure.
- Check work packages. Create your work packages so they are completely independent of other work packages. Make sure that individual tasks are not duplicated across your structure. This recommendation aligns with two widely used guardrails: the "100% rule" (your WBS captures 100% of the project scope and nothing extra) and "mutual exclusivity" (no deliverable or subtask appears twice, preventing double-counting of work, cost, or time).
- Stay outcome-focused. Keep the structure centered on deliverables and measurable milestones rather than action lists (e.g., "braking system" rather than "calibrate brake pads").
Aim for the right depth. Many WBS diagrams fall into three levels of detail overall, though some branches may need more subdivision than others to make the work truly manageable.
Types of work breakdown structures
There are two types of work breakdown structures commonly employed in project management: the process-oriented WBS and deliverable-oriented WBS. Contrary to popular belief, both structures can (and should) be used when defining your project scope. Used in tandem, they can offer unique and valuable insights into the project management process.
Process-oriented work breakdown structure
A process-oriented WBS defines a project in terms of steps, work phases, or functions. This type of WBS focuses on the steps that need to be taken within individual disciplines to complete a project and typically phrases individual elements in the verb form.
The benefit of using a process-oriented WBS in tandem with your deliverables-oriented WBS is that it provides a thorough breakdown of work from a functional perspective, creating a more coherent project scope. It can also be used to ensure high-quality processes are established throughout your project.