PERT Charts: What They Are and How to Use Them

What is a PERT chart?

Programme evaluation and review technique, known as PERT, is a tool that helps improve how you plan resources for specific tasks in large-scale or complex projects, understand milestones, estimate task durations, and organise project scope. 

Milestones in a PERT chart are represented by boxes or circles called nodes, linked with arrows that symbolise task order. For example, you can only paint a room once you've cleaned it, so cleaning would be listed as the first task and painting as the second. 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 visual tool. By simplifying complicated projects and clarifying dependencies, your PERT chart improves collaboration between departments and experts by offering a common reference point. The chart can also help you explore hypothetical scenarios to see what would happen if you made changes during the project.

Simplify complex projects.

Complex projects often have multiple teams or departments working on related tasks. A PERT chart helps you visualise 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 visualise and prioritise 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. 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 different scenarios to determine which ones are most likely to occur and the consequences if they do.

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.

PERT chart vs. Gantt chart

PERT and Gantt charts are both visual tools that help you plan projects. They allow you keep your team organised and on track. PERT charts help you understand task dependencies. Gantt charts work best when tasks are clearly defined with a clear beginning and end date. 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 it to create your Gantt chart. They are complementary tools.

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 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 better understand tasks and the critical path. 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 all parties have the same goals. 

PERT charts visually represent the required resources for each task to help eliminate overbooking resources. It provides a top-level view of your project, which may be the best way to understand the complexities of a new project. 

Maximise resources.

PERT charts help you identify delayed areas in your project so that you can assign more people or better equipment for those tasks. You can also pinpoint areas where you have excess capacity, thus freeing up resources for other jobs.

Improve project visibility.

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.

Visualise new or complex projects.

If you've never done a particular project, a PERT chart makes it easier to visualise 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.

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, analyse, 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 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 organise them logically. 

You'd make the initial PERT chart after creating your team and the work breakdown structure (WBS). The WBS creates all the tasks added to the PERT chart. 

How to make a PERT chart

Here are five logical steps for creating a PERT chart:

1. Identify project tasks.

Review the project plan and 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 the 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.

You should use three numbers to estimate each task's time frame: optimistic (O), pessimistic (P), and most likely (M). You can determine the expected duration of each activity by adding the three estimates together and dividing by three. You can use this number to estimate 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.

Increase your project management toolkit.

Project management is the art and science of planning, organising, and managing resources to complete a specific project on time and within budget. As a project manager, myriad tools are available 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 programme on Coursera.