The Work Breakdown Structure (WBS) is defined by A Guide to the Project Management Body of Knowledge Sixth Edition (PMBoK® Guide) as: A deliverable-oriented hierarchical decomposition of the work to be executed by the project team to accomplish the project objectives and create the required deliverables. Don’t get scared by this long jargon. Basically, what it means is Work Breakdown Structure is a breakdown of work into as small a task as possible. It will look like the common file explorer (tree diagram) that we use in our computer Window operating system.
The main purpose of Work Breakdown Structure is that firstly, it helps to define and organize the scope of the total project more accurately and specifically. The most common way this is done is by using a hierarchical tree structure. Each level of this structure breaks the project deliverables or objectives down to more specific and measurable chunks. The second reason for using a Work Breakdown Structure in your projects is to help with assigning responsibilities, resource allocation, monitoring the project, and controlling the project. The WBS makes the deliverables more precise and concrete so that the project team knows exactly what has to be accomplished within each deliverable.
This also allows for better estimating of cost, risk, and time because you can work from the smaller tasks back up to the level of the entire project. Finally, it allows you double check all the deliverables’ specifics with the stakeholders and make sure there is nothing missing or overlapping. Besides, using the tree structure, you may also use Mind Mapping methodology, if you are familiar with it.
The first step to creating your WBS is to get all your team, and possibly key stakeholders, together in one room. Your project team is your most vital asset to this process. Your team possesses all the expertise, experience, and creative thinking that will be needed to get down to the specifics of each deliverable. Next, we have to get the first two levels setup. The first level is the project title, and the second level is made up of all the deliverables for the project. At this stage it is important to function under The 100% Rule. This rule basically states that the WBS (specifically the first two levels) includes 100% of all the work defined in the project scope statement and management plan. Also, it must capture 100% of all the deliverables for the project including internal, external, and interim. In reality the WBS usually only captures between 90-95%, but 100% is our goal.
Once we have gotten the first two levels set, it is time to launch into our decomposition or breakdown. Decomposition is the act of breaking down deliverables in to successively smaller chunks of work to be completed in order to achieve a level of work that can be both realistically managed by the Project Manager and completed within a given time frame by one or more team members. This level of breakdown and detail is called the Work Package. Work packages are the lowest level of the WBS and are pieces of work that are specifically assigned to one person or one team of people to be completed. This is also the level at which the Project Manger has to monitor all project work.
The very common question is how specific or small does a chunk of work need to be to still be considered a work package? Well PMBoK® Guide does not seem to give a definitive answer on that. Most project managers concur that this varies by project, but can usually be measured using the 8/80 Rule. The 8/80 Rule says that no work package should be less than 8 hours or greater than 80 hours. Notice we said that the work package is the lowest level of the WBS. Activities and tasks are not included in the WBS. They will be planned from the work packages once they are assigned.