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What is a PERT Chart? (+Instructions and Best Practices)

December 6, 2018

If you work in project management, you understand the importance of an effective project management strategy or methodology.

We’ve already delved into other aspects of project management, like how to make use of Gantt charts and the pros and cons of different project management methodologies. But it’s worth it to take a deeper look at other methodologies and understand how they could have an impact on your team.

This time around, let’s get ready to discuss PERT charts.

What is a PERT chart

PERT is an acronym which stands for program evaluation review technique. This methodology originated from the US Navy in the 1950s and is still being utilized by many teams for project management today.

original pert chart example

The PERT method is similar to CPM or the critical path method in that they both aim to schedule and direct projects.

PERT charts are typically used before a project begins so administrators can understand the duration of the project as a whole. While they don’t have to operate off of specific dates like a Gantt chart would, they should still be just as accurate in their estimates of task duration.

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The chart, or network diagram, itself is a schematic or visual diagram of a project’s schedule. PERT charts make use of network diagrams to represent the schedule. They are made up of two parts: nodes and vectors.

The nodes represent tasks while the vectors represent the order in which the tasks are completed.

In the sample image below, the circles are nodes and the lines are the vectors. So the circles represent tasks one, two, and three whereas the lines represent the order of steps, as well as the time taken to completion.

In this example, it takes two days to advance from step one to two, and three days to advance from step two to three.

 

Pert Chart example

PERT charts are also known as “precedence diagrams” because they show both the order in which tasks must be completed, and they communicate dependencies.

Consider the example above. Because steps two and three are only dependent on step one, they can be accomplished at the same time. These are referred to as parallel or concurrent tasks. Tasks that have to be completed in a certain order are called dependent or serial tasks.

In the Gantt chart example below, you can see there are dependent tasks. 

PERT chart dependent tasks

PERT charts help users develop a realistic idea of the project’s timetable. Administrators accomplish this by assigning three possible timelines to each task: optimistic, pessimistic, and most likely.

The optimistic estimate is your best case scenario, assuming all goes well. Your pessimistic estimate is the maximum amount of time it could take to accomplish one activity, or your worst case scenario. Typically only the “most likely” estimate is delivered to members of upper management.

How to create a PERT chart

In order to create a PERT chart, you need to remember two simple guidelines. First, you should represent tasks as arrows. Second, you should represent milestone dates as nodes, which are typically visualized as circles or rectangles.

If you look at a PERT chart in relation to one activity, you can see how simple they are to understand. Let’s do this using the sample image below.

Single activity PERT chart example

The node on the far left labeled “one” indicates the first task in a series. Because we’re looking at a single activity, I’ve gone ahead and labeled the names of the tasks on the chart.

The design of your PERT chart will depend entirely on you and your team’s preference. Some choose to keep the chart very minimal and label tasks elsewhere, such as in a spreadsheet or list. Others use what is called an activity-on-node design wherein more detailed descriptions of tasks are included in the chart.

Lucidchart provides a helpful PERT chart example of the activity-on-nodes type of PERT chart, should that be your preference.

Step 1 in this example is researching a topic. I’ve indicated that this research will take one day. PERT charts will always feature the numerical duration of a task on top of the line/arrow connecting the two tasks. Your chart should feature a key denoting how you are measuring time (ie hours, days, weeks, etc).

PertChart for a single activity

Task two is dependent on task one. The creator in this scenario cannot move onto their outline until they have completed topic research.

Full PERT chart example

When you add more tasks to the mix, PERT charts begin looking more complex and the brain can find them difficult to interpret.

That’s why we started small, so seeing a larger example wouldn’t completely fry us. Now that we understand how to interpret one activity, let’s move on to a more in-depth example.

In this example, we have five tasks. Task four is dependent on the completion of tasks two and three, while task five is independent of all tasks except for the first one. Once you’ve completed task four and five, you arrive at the finish line.

Pert Chart example 2

PERT chart best practices

I’ve given you a few generic examples of PERT charts, but there’s still so much to know! In this section, I’ll outline some commonly understood best practices of PERT charts to help you get the most out of this strategy.

  • PERT charts should be created prior to the execution of a project. PERT charts are a data visualization and planning tool that help project administrators understand the amount of time a project is going to take.

    While they continue to be used throughout the duration of a project, managers should be proactive in drafting a PERT chart before other work begins. This way, project managers can prepare for issues and adjust expectations accordingly.

  • For larger projects, create break-out PERT charts. Some projects span across multiple teams and departments. Trying to follow a PERT chart that communicates the responsibilities of 50 people will only serve to give your team headaches.

    It is a better idea to take that large chart and break it out into smaller charts that can be dispersed among teams. This lets a team know their individual responsibilities and timelines without overwhelming employees with too much information.

  • Use PERT charts in conjunction with Gantt charts. Many professionals try and ask the question, “Gantt chart or PERT chart?” A good answer is “both.” PERT charts and Gantt charts both show a project’s timeline, but they take different routes to get there.

    Gantt charts keep projects on schedule, but PERT charts give the project a schedule in the first place. The common opinion is that a strong strategy makes use of both project management methodologies.

  • Don’t over-node your PERT chart. A PERT chart with too many nodes is overwhelming and near impossible to read. For best results, keep your charts limited to 20 nodes or less.

    Think of which tasks really need to be represented on the chart, and which can be consolidated into each other. Additionally, think of how you could break the chart up into break-out charts. Remember, these charts are worthless if your team cannot understand them!

  • Create PERT charts using the tool you are most familiar with. There are specific tools for creating PERT charts, or you could use an Excel spreadsheet. Whatever you choose, make sure it’s something both you and your team understand.

    These charts are important to understanding and managing a project, and you don’t want to struggle trying to understand the software itself. It’s also possible you’ll have to go in and make changes upon receiving feedback. The better you understand your software choice, the easier this will be.

PERT chart software

As I stated in PERT chart best practices, you should create PERT charts within a solution you understand how to operate.

For many, this tool might be Microsoft Excel, as it’s frequently used regarding other business functions and wouldn’t take too much getting used to.

For those who have never used Excel and would like to make a PERT chart specifically, there are other solutions to consider. Many project management solutions will also offer chart creation features. 

Another option you have is to consider specific chart-making tools such as LucidChart or WBS Schedule Pro.

Uncharted territory

If PERT charts are new for you, don’t worry! They’re an effective scheduling and project management tool that, through time and practice, will become second nature for you to create and for your colleagues to understand.

And if you’re looking for more information to help with your project strategies, I’d recommend reading more on project milestones and why they matter.

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