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Difference between Work Breakdown Structure (WBS) and Resource Breakdown Structure (RBS)

Difference between Work Breakdown Structure (WBS) and Resource Breakdown Structure (RBS)

Work breakdown structure is an important deliverable for any project. Through the WBS, the project manager is in a good position to categorize the work that the team needs to accomplish into small sections that can be managed easily whereas RBS is considered an important part of efficiency when it comes to project management. Through RBS, the project manager is able to compile a list of resources needed to accomplish a given task in hierarchical order.

What makes RBS different from WBS

WBS is a visual representation of the entire scope of the work to be done, broken down into smaller segments that each member of the project team is able to understand. This is because, with each of the completion levels, there are definitions and details relevant to that phase. On the contrary, RBS can be broken down into geographical resources or organizational resources. Some of the other tools that are necessary for proper and efficient RBS include resource estimation, a resource calendar, and activity lists.

The reason behind this is because when you are managing any project, you will have to work with different project components and project resources in order to complete the project. A good example is the members of your project team.

You must make sure they are productive and strategically poised through the life of the project you are undertaking.

Now, in case you are planning on coming up with a WBS that is efficient, the following are some of the important guidelines that will help you see this through:

  • The project/final deliverable is always at the top level
  • You do not always have to define all the elements at the same level
  • The work groups should not take up more than 10 days
  • Each work group must be independent
  • There should be no duplication in the work groups all through the structure

The following is a simple representation of a segment of a WBS for building a house:

Building a House

                                              Foundation                     Interior                       Exterior

Completion                         24%                                      45%                                 30%

Budget                               $50,000                              $86,000                          $72,000

It shows different parts of the project that are to be carried out and provides more information about the budget needed for them, and the level of completion.

A WBS, therefore, is a map/outline of a specific project. The main project is the key deliverable in a WBS, and from there, it is broken down into smaller sub-categories, each with specifics of how they will be delivered upon.

On the other side, talking about RBS, you must know that it functions using some of the important tools. The project managers are instructed to employ or execute an efficient RBS by using these tools. These are as follows:

  • Activity list

This is a list of all the activities that are key to the completion of the project. The project manager does not just need a list, they need to get as much information as conceivably possible about these lists too. This information will also include the resources that the activities listed consume.

  • Resource estimation

For each activity to be accomplished in a productive, efficient and more importantly, cost-effective manner, the project manager must estimate the volume, type and variety of resources that are needed.

If these estimates are skewed, it might be impossible to achieve the objectives of the project, or as a whole, the project could fail.

  • Resource calendar

A resource calendar is about the availability of resources over time. The project manager will need a list of all the resources that are needed to complete the project.

These resources must also be listed based on their availability over the long term. This information is important for the project manager to ascertain whether the resources needed will be available during a specific time, so the project does not stall.

At the moment, RBS is becoming more and more important, with project management software incorporating it into their structure. If you are using any project management program, you can log in and check the availability of the resources you need, and more importantly how they are classified.

This generally helps the organization in the sense that the project managers are able to view a lot of details from a simple database, about all the resources being used.

Importance of a WBS vs focus of RBS

There are several key benefits that the project manager and the project team can derive from a WBS, other than organizing and defining the work needed to complete the project. Through the WBS, it is easier to allocate a budget from the top tiers of the structure. Once this is done, the budgets for each department can be structured based on the breakdown in the WBS.

Cost and time estimates are usually provided for each WBS section. By doing this, it is easier to work out a schedule and appropriate budget for the entire project.

Through a WBS, it is also easier to keep track of the performance of individual project sectors. The project manager is in a good position to tell the performance cost of the project, identify problem areas and more importantly the key issues in organizing the project. Conversely, in RBS, the emphasis on a hierarchical listing of resources is key. You need to list all the resources, whether they are significant or even if to you, they seem redundant. Each of the levels of the project will need a certain number of resources. These have to be listed according to their importance towards the completion of each level, and finally completing the entire project.

The resources listed are then subdivided into smaller categories of the type of resource they are, to help the project manager in classification. Classification will actually proceed further into different sub-groups until each of the types of resources has been grouped into single entities that are easier to identify and manage.

Benefits of WBS versus RBS

One of the benefits of a WBS is that it helps the project manager determine any potential risks that a project might have. In case there is any branch of the project that has not been clearly defined, it becomes a risk area that has to be addressed. Such risks are supposed to be tracked properly, and a careful review provided as the project goes on.

In case the project seems like it is falling behind schedule, it is easier for the project manager to refer to the WBS and identify the areas that are struggling, and make the appropriate decision to turn things around. In contrast, the immediate benefit of RBS, especially the breaking down of resources into sub-groups is to ease the work of management centers. Supervision becomes much easier and a lot of time is saved in the process.

The supervisors are able to track each resource group as they proceed with the project. It is easier to expedite certain levels of the project without relying on others, having apportioned the right resources to their completion. Therefore, some projects can easily be completed before the set deadline, especially if the completion of different levels of the project is not co-dependent.

With a good RBS plan in place, the management is also in a good position to get a good picture of the total number of resources that are available for each of the participating teams. Other than understanding the resources available, they are also able to manage how the resources will be utilized.

Comparing the above information, it is advisable to assign colors to the different sub-deliverables in a WBS. This is important to get a heat map of the progress of the entire project. It will also make it easier to get the attention of management on project areas that are complete and the ones that are slacking.

The WBS, when handled properly, is a good way to boost the productivity of the teams working on the project, and see the project completed on time. The project manager is able to identify the necessary skills to enable them to complete the project in good time but when it comes to RBS, we must understand the types of it. The conventional type of RBS is an organizational RBS. The hierarchical organizational systems that are already established usually help to create this RBS. The resources in an organizational RBS are usually distributed based on the needs of each organizational department and workgroup. These are categories that have actually been defined and set by the organization.

Geographical RBS is in most cases unconventional. The main concern of a geographical RBS is the distribution and/or location of the resources in question, and how they are allocated in different locations, depending on the needs of the organization.


In conclusion, both the WBS and RBS are key to the successful completion of a project, and efficiency of the relevant project teams. The following are the key points that define either of the structures.

Work Breakdown Structure Resource Breakdown Structure
o   Groups the work into categories o   Groups resources into categories
o   Helps in project progress supervision o   Helps in supervision of resource use
o   Project groups must be independent o   Resource groups can depend on each other
o   Emphasis on project timeline o   Emphasis on resource allocation

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