What is a PERT chart?

A PERT chart, or Program Evaluation and Review Technique, visually represents a project’s timeline and the individual tasks necessary for completing the project. Similar to Gantt charts but with a different structure, a PERT diagram walks you through a project’s start and end date by plotting its stages graphically. PERT project management helps you assess the time required to complete a project, calculate project risk, and analyze task dependencies. These charts also provide estimates relying on optimistic, pessimistic, and expected timelines.

How are PERT charts and Gantt charts different?

Both charts offer a graphical view of a project’s schedule, tasks, and timelines, but they have a few significant differences.

PERT charts

PERT charts, proposed by the US Navy in 1957 but only widely used 30 years later, use the critical path method to illustrate the longest path through a project. The critical path method (CPM) assesses the earliest and latest project completion dates and the earliest start date, determining the minimum time required for the entire project. This time management technique seeks out directly related activities and calculates their duration from start to finish based on dependencies. When an activity doesn’t have a dependency, it doesn’t add any delay to completing other tasks. When dependencies exist, these tasks become critical activities or critical paths.

PERT charts are free-form diagrams ideal for project planning with multiple milestones, tasks, or deliverables. Project managers create PERT charts using boxes or circles (nodes), each representing a milestone or event. They connect them with directional arrows, each representing sequential tasks between milestones and the time it takes to complete each one. A diverging arrow indicates activities you can complete in no particular order, as they don’t have any dependencies.

Gantt charts

Gantt charts, developed in 1910 by Henry Gantt based on Project Management Theory, displays each project task linearly. A linear view gives you a snapshot of the expected durations and chronological order of each task and the overall project. Gantt charts also illustrate the teams and individuals responsible for each job. While these bar graphs (horizontal and vertical lines representing time, tasks, and subtasks) show your project’s intended schedule, they don’t indicate how well the project is progressing or task dependencies.

When to use a PERT chart

Many project managers use PERT charts to assess and complete projects. The PERT diagram is a simple way to estimate timelines, evaluate resources, and determine the critical path of a project:

• Estimating timelines: The PERT diagram is invaluable for understanding expected timelines during your initial project planning phase because it assesses individual tasks and overall project duration.
• Evaluating the resources: A PERT chart displays tasks that require additional resources and those that don’t, which saves both you and your stakeholders time by having crucial information up front and easily accessible.
• Determining the critical path: One of the crucial elements of a PERT chart is having the ability to calculate your project’s critical path—an essential part of visualizing your project’s overall timeline.

How to create a PERT chart template

A basic PERT chart template consists of a start and end date and various project tasks, each with its own start and end dates, and the following drawings:

• Numbered nodes (circles): Each numbered circle represents a project milestone or event, stage completion, or series of tasks to move the project forward.
• Directional or concurrent arrows: These PERT chart arrows represent the activities or tasks you must complete before moving on to the next project event or phase. Project managers use directional or concurrent arrows to schedule tasks with dependencies, indicating sequential activities.
• Divergent arrows: These arrows point to any task your team can work on simultaneously or in any sequence they choose, as these activities don’t have dependencies.

How to plot information on your PERT diagram

Now that you know how to create a template, follow these steps to make the most of your PERT diagram:

Identify project tasks

Collaborate with your team to define all the significant milestones, phases, and tasks necessary for successful project completion. Begin your project planning stage the same way you’d start your initial project management phase, which may look like this:

• communication plan
• initial kick-off meeting
• business case

Early planning helps you define dependencies and connect tasks throughout the subsequent phases.

Define dependencies

Often referred to as logical relationships, task dependencies help you track work, establish clear communication, and ensure successful task completion. For complex projects, plan project durations and timelines ahead of time. After defining task dependencies, plot them on your chart using directional arrows to show the order sequence. This high-level visualization strategy shows all the work your team needs to complete.

Connect your tasks

Group your milestones and events (numbered nodes or circles) according to similarities. Add all the tasks and activities your team must complete between each node. Use directional or divergent arrows to connect your tasks accordingly.

Estimate project timelines

Use the critical path method and PERT formula to estimate your overall project timeline. The critical path is the longest sequence of tasks your team must complete to finish a project successfully. Your objective is to find the path that will take the most time to complete so you can estimate the shortest project duration. Calculate your estimates based on the following factors:

• Optimistic time: The best-case scenario or least time to complete a task.
• Most likely time: The most likely scenario or best guess at how long a task will take.
• Pessimistic time: The worst-case scenario or maximum time to complete a task.

Use the PERT formula to calculate expected task durations using:

(Optimistic time + (4 × Most likely time) + Pessimistic time) ÷ 6

Your measurements can be in minutes, hours, days, or weeks. For example, if your optimistic time is 20 minutes, your pessimistic time is 40 minutes, and most likely time is 30 minutes, your PERT formula would look like this:

(20 min + (4 × 30 min) + 40 min) ÷ 6 = 30 minutes

Once you calculate the expected time per task, add all your estimates to get an average project timeline. Your calculation should typically fall between 80% and 120%. If not, revise your estimates. Write the time frame or deadline to complete all activities along your arrows.

Manage task progress

The last step in charting your PERT diagram is updating it as changes occur. Do this by mitigating issues and closing dependencies until you complete all project tasks and milestones. You can pair your updates with a change control process to help map and communicate project changes to all team members. Once you complete all tasks within a project, archive your materials in a shared space so your team can refer back to them when necessary.

PERT chart benefits

PERT charts are a time management tool that helps complete project tasks within timelines and deadlines by calculating risks and grouping dependencies. There are other benefits of using a PERT chart for project planning:

• promotes collaboration and coordination between departments
• optimizes a project’s completion time rather than focusing on cost optimization
• manages uncertainty by factoring in all project details to estimate timelines for tasks and activities
• gets a bird’s eye view of your project’s entirety to identify potential obstacles or bottlenecks from the start
• determines the individual and team roles throughout the project, creating accountability and ownership of tasks
• enables you to understand how each task fits within a project’s timeline
• calculates the most likely time frame for completing tasks, activities, and projects
• less chance of things falling through the cracks, as the PERT chart shows every step of a project’s lifeline
• creates reasonable milestones
• shows full transparency for everyone working on the project
• creates a strong foundation from the planning phase to your expected results
• sets project benchmarks and goals that help you stay on track or redirect when necessary
• gives you clarity and confidence knowing your projects are running on schedule