What Is a PERT Chart?

A PERT chart is a project management tool that provides a graphical representation of a project's timeline. The Program Evaluation Review Technique (PERT) breaks down the individual tasks of a project for analysis. PERT charts are considered preferable to Gantt charts because they identify task dependencies, but they're often more difficult to interpret.

How Do PERT Charts Work?

A PERT chart uses circles or rectangles called nodes to represent project events or milestones. These nodes are linked by vectors, or lines, that represent various tasks.

Dependent tasks are items that must be performed in a specific manner. For example, if an arrow is drawn from Task No. 1 to Task No. 2 on a PERT chart, Task No. 1 must be completed before work on Task No. 2 begins.

Items at the same stage of production but on different task lines within a project are referred to as parallel tasks. They're independent of each other, but they're planned to occur at the same time.

Fast Facts

  • PERT charts were first created by the U.S. Navy's Special Projects Office in 1957 to guide the Polaris nuclear submarine project.
  • A PERT chart uses circles or rectangles called nodes to represent project events or milestones. These nodes are linked by vectors, or lines, that represent various tasks.
  • A PERT chart allows managers to evaluate the time and resources necessary to manage a project.

A Real World Example of a PERT Chart

PERT charts were first created by the U.S. Navy's Special Projects Office in 1957 to guide the Polaris nuclear submarine project. They've since been used all over the world and in numerous industries. A well-constructed PERT chart looks like this:

Interpreting PERT Charts

A PERT chart is a visual representation of a series of events that must occur within a project’s lifetime. The direction of arrows indicates the flow and sequence of events required for project completion. Dotted activity lines represent dummy activities—items that are located on another PERT path. Numbers and time allotments are assigned and shown inside each vector.

These charts have their own definitions and terms, the most important of which anticipate how long it will take to finalize a project. "Optimistic time" refers to the shortest duration, and "pessimistic time" is logically the longest it might take. The "most likely time" indicates a reasonable estimate of the best-case scenario, whereas "expected time" accounts for problems and obstacles.

The Benefits of PERT Charts

A PERT chart allows managers to evaluate the time and resources necessary to manage a project. This includes the ability to track required assets during any stage of production in the course of the entire project.

PERT analysis incorporates data and information from multiple departments. This encourages department responsibility, and it identifies all responsible parties across the organization. It also improves communication during the project, and it allows an organization to commit to projects that are relevant to its strategic positioning.

Finally, PERT charts are useful for what-if analyses. Understanding the possibilities concerning the flow of project resources and milestones allows management to achieve the most efficient and useful project path.

The Disadvantages of PERT Charts

The use of a PERT chart is highly subjective and its success depends on management’s experience. These charts can include unreliable data or unreasonable estimations for cost or time for this reason.

PERT charts are deadline-focused and they might not fully communicate the financial positioning of a project. Because a PERT chart is labor intensive, the establishment and maintenance of the information require additional time and resources. Continual review of the information provided, as well as prospective positioning of the project, is required for a PERT chart to be valuable.