What is a PERT Chart?

Program Evaluation and Review Technique (PERT) is a graphical representation of a project's timeline. It breaks down tasks and analyzes how much time they will take to complete. A PERT chart also helps in identifying an estimated time to complete the project. The term used for this is the critical pathLongest sequence of activities from the starting milestone to the finishing milestone..

PERT chart symbols

When do we use the PERT chart?

PERT Charts help deal with time-sensitive projects with tasks dependent on each other. This way, the team will have a clear direction and be ready for whatever comes their way. However, PERT charts are unsuitable for long-term projects as they will require many changes, which might require more staff. It will become difficult to track the progress of the project.

How to make a PERT chart

There are a few ways we can make a graph. A common way contains two elements:

1. Nodes

2. Arrows

Steps to create a PERT chart

1. First, we identify project activities. Then define the tasks and milestones involved.

2. Second, we add dependencies. We represent this by directional arrows. The arrows will identify the sequence of the tasks.

3. Third, we add a time estimate. We can use estimated time frames or deadlines for each activity.

4. Finally, we draw the PERT chart. We write the activities between nodes and connect them with directional or divergent arrows.

Terminology

A few terms that one should know to implement PERT properly are as follows:

• Milestone: It indicates the start or end of a task or several tasks. We represent these by circles that are often numbered.

• Tasks: A task is an activity that requires time and resources. Either directional or diverted arrows represent these. There are two types of tasks:

  1. Predecessors: Tasks that come before a milestone

  2. Successors: Tasks that follow a milestone

• Critical path: The longest path from the starting point to the ending point. A critical path helps mark an estimate of the total duration of the project. 

• Time: We usually write the time estimates below the arrows. PERT allows us to use four different ways to estimate the time required to complete each task: 

  1. Optimistic time (o): The minimum time required to complete a task.

  2. Pessimistic time (p): The maximum time required to complete a task.

  3. Most likely time (m): The best possible estimate of the time required to complete a task without considering the risks.

  4. Expected time: The best possible estimate of the time required to complete a task while keeping the risks.

The formula used to calculate the expected time is as follows:

Where $o$ is optimistic activity duration, $p$ is pessimistic activity duration, and $m$ is most likely activity duration.