PERT Charts: What They Are and How to Use Them

What is a PERT chart?

Program evaluation and review technique, known as PERT, is a project management tool that helps you do the following:

• Plan resources for specific tasks in large-scale or complex projects

• Understand milestones

• Estimate task durations

• Organize project scope

Milestones in a PERT chart are represented by boxes or circles called nodes. Nodes are linked together with arrows that symbolize task order. For example, you can't paint a room until you've cleaned it, so cleaning would be listed as the first task and painting as the second one. The nodes and task lines on the PERT chart may contain information about each task and event milestone, including:

• Name and ID

• Type of activity (category or department)

• Task owner

• Expected duration (optimistic, pessimistic, expected)

• Earliest start time

• Latest start time

• Milestones

• Any additional notes

What is a PERT chart used for in project management?

PERT charts are typically used on large projects with many moving parts, but even small, complex projects can benefit from this type of visual tool. Here are some PERT chart benefits:

Simplify complex projects.

Complex projects often have multiple teams or departments working on related tasks. A PERT chart helps you simplify complex projects and visualize what everyone is doing so it's easier to understand how the different pieces fit together. 

Clarify task dependencies.

Your PERT chart can help you clarify task dependencies. You can visualize and prioritize which tasks need to be completed first or done concurrently, who is responsible for completing each task, and how long each task will take.

Aid collaboration between departments.

You may need to bring multiple departments and subject matter experts together on large or multi-faceted projects. Your PERT chart improves collaboration between departments and experts by offering a common reference point. PERT charts help you see the big picture, understand who is responsible for what and when, and the best way to do the job.

Explore hypothetical scenarios.

An important aspect of project management is assessing risk and planning accordingly. A PERT chart can help you explore hypothetical scenarios to determine:

• Which scenarios are most likely to occur

• Potential consequences of different scenarios

• The effects of making changes during the course of the project

For example, if your project involves building a new website, you may want to create a PERT chart with multiple possible scenarios that could impact your product’s cost, time, or quality.

Maximize resources.

PERT charts provide a visual representation of the required resources for each task. PERT charts help you:

• Eliminate overbooking resources.

• Identify delayed areas in your project so that you can assign more people or better equipment for those tasks.

• Pinpoint areas where you have excess capacity and thus free up resources for other jobs.

Improve project visibility.

PERT charts provide a top-level view of your project, which may be the best way for you to understand the complexities of a new project. The nature of the PERT chart allows everyone involved in the project to see the big picture and to understand how their work fits into the overall process. This is particularly helpful when you manage remote teams.

Visualize new or complex projects.

If you've never done a particular type of project before, a PERT chart makes it easier to visualize how all the pieces fit together. This gives you a better understanding of what's needed to prevent problems at each stage before they happen.

Form a definite completion time.

Without a PERT chart, determining completion time is an educated guess based on experience with similar projects. A PERT chart can give your estimate more weight and make it easier for upper management to budget for the project and allocate resources based on your schedule.

PERT chart vs. Gantt chart

PERT and Gantt charts are both visual tools that help you keep your team organized and on track. Here are some distinctions to keep in mind as you plan projects:

When used together, these charts can complement one another and provide more insight into a project's potential. Typically, you’ll use a PERT chart to help you map out all of the tasks and milestones involved in a given project, then use the PERT chart to create your Gantt chart.

Read more: Gantt Charts: What They Are and How to Make Them

PERT chart vs. CPM

A PERT chart is an activity and milestone-focused, probabilistic tool, whereas the critical path method (CPM) is a deterministic chart that’s task-focused, and more suited to predictable projects. At the same time, they share similarities. PERT and CPM chart diagrams look alike. Both tools derive from the critical path idea, which maps the essential series of duties to complete your project. However, each approach differs by project scenario.

Here is a side-by-side comparison of the PERT and CPM charts:

PERT charts are excellent for situations where activities and timeframes are unpredictable, and if you want to understand tasks and the critical path better. Successful projects are typically well-planned. A project plan outlines a project's:

• Deliverables

• Milestones

• Resources

• Timeline

It helps you manage a project's progress from beginning to end and ensures that all parties have the same goals.  

Considerations for using PERT charts

There are several factors to consider when using PERT charts in project planning:

• The nature of the PERT chart and its information means it’s rarely possible to create, analyze, or update a PERT chart in isolation. You’ll need to be prepared to work as part of a larger group to develop and use this tool.

• PERT charts can quickly become very complex due to the large amount of information they contain. You’ll need to learn how to update, modify, and maintain the PERT diagram to avoid losing its power as a planning tool.

• As with any planning method based on probability and uncertainty, the subjective basis of some decisions can be challenging. It takes experience to create PERT charts that offer value in a project.

When to use a PERT chart

PERT charts are most helpful to you in the project initiation and planning stages of the project lifecycle, such as when you determine task interdependencies, estimate project timelines, and choose the project's critical path. You can use PERT charts to plan and schedule complex projects with many tasks because they’ll help you organize the tasks into a logical structure. 

After creating your team and the work breakdown structure (WBS), you’d make the initial PERT chart. The WBS is used to create all the tasks which are added to the PERT chart. 

How to make a PERT chart

Here are five steps for creating a PERT chart:

1. Identify project tasks.

Take a look at the project plan and review the results-oriented work packages (milestones) you identified in your WBS. These will be the individual nodes in your PERT chart. 

2. Define task interdependencies.

Review the tasks you have identified for the project. Some tasks might be completed independently, but others will need other tasks completed before they are started. Identify which tasks are dependent so this information can be reflected in the PERT chart.

3. Connect project tasks.

Connect your project tasks with arrows showing dependencies and the direction of the flow. You’ll need to learn common symbols, representations, and other notations that are best for PERT charts.

4. Estimate task, milestone, and project timeframes.

Estimating the timeframe for each task will help determine milestone timeframes and the overall project time. A good PERT chart will show you which tasks need to be expedited and which ones can be delayed without impacting the general timeline of your project.

To estimate each task's time frame, you'll use the PERT formula. Start by quantifying these time values in units such as days or hours:

• Optimistic time (O): the least amount of time required to complete a task

• Pessimistic (P): the maximum amount of time required to complete a task

• Most likely (M): an estimate of the time a task will take without any delays or problems.

Then, use this basic PERT equation to determine the expected time (E):

E = (O + 4P + M) / 6

Estimated time equals optimistic time value, plus the pessimistic time value multiplied by four, plus the most likely time value, with this sum divided by 6.

For example, imagine you're building a website. You might say that the best case scenario is that the project takes ten days (O), with no delays or problems. Worst case, it takes twenty days (P). Most likely, it will take fifteen days (M). Using the formula:

E = (10 + 60 + 20) / 6

E = 15 days

Use your estimates to forecast when you'll reach key milestones and to determine whether your project is on track. You can also look at pessimistic values to develop a confident completion date, which should hold even if things don’t go as planned.

5. Manage task progress.

Track your progress and make adjustments to ensure your project stays on schedule. You’ll probably use a combination of a PERT chart and a Gantt chart during the execution stage of the project lifecycle.

Build your project management toolkit

Project management is the art and science of planning, organizing, and managing resources to complete a specific project on time, and within budget. As a project manager, there are a variety of tools available to you to execute your projects. If you'd like to enhance your skill set and earn a Professional Certificate for your resume, consider taking the Google Project Management: Professional Certificate program on Coursera.