The PERT Diagram: Save Time with this Project Management Chart

The PERT Diagram: Save Time with this Project Management Chart

By Nathan Cavet
Published: 07/06/2021

The PERT diagram (or PERT chart), like the Gantt chart, is a major tool in the project management process. PERT was developed in the late 1950s for the Polaris nuclear submarine project of the US Navy. It would have allowed the Navy to save two years of development time. So, intrigued by this project management tool?

What is the PERT diagram? How do you build it?

Don’t panic, Appvizer explains in this guide how to avoid wasting time with PERT!

What is a PERT chart?

The PERT (Program Evaluation and Review Techniques) diagram is a project planning and management tool. Its graphic form represents a program (here synonymous with a project) illustrated by nodes and arrows that connect in order to:

  • determine the essential steps of a project,
  • improve the schedule if necessary,
  • review the progress once the project is underway.
Circled tasks are the critical path© Lucidchart

The PERT diagram allows you to identify potential connections between all the tasks in a project. It is useful when activities can be conducted in parallel rather than in sequence.

💡 It is simple to confuse the PERT chart and the Gantt chart. Despite the fact that both contribute to your project development, they are distinct:

  • The PERT chart is usually used before the start of an ambitious project to break up the less important tasks. It is work that is done beforehand in a process of task planning and optimization.
  • The Gantt chart is used more during a project. It is used to organise the tasks by time and to follow how the project progresses.

Why use a PERT? 3 main advantages

The PERT diagram brings several advantages to facilitate project management and save time. It allows to:

  • Simplify complex projects by helping project managers or project portfolio managers to better master ambitious projects.
  • Involve multiple departments and experts at the same time: PERT is an organizational tool that extracts data from each department working on the project.
  • Explore different eventualities by creating what-if scenarios. You define the time and resources needed for a project for each scenario and see what can and cannot work.

The 6 steps to building a PERT chart

Got a big new project coming up? The PERT chart intrigues you, and you want to try it? Follow our guide and the steps to learn the different techniques to use it!

1 - Prepare the tasks

The first step in your project is to list all the tasks (or events) required for your project. Based on the same principle as the To do list, this list allows you to better manage the different ideas... and to not forget anything!

It is necessary to identify them and to estimate the duration of each one. It is also necessary to see if some of them can be linked. If you determine that certain tasks or activities are dependent on each other, you will also want these tasks to be done together.

Finally, it is important to represent the precedence of the tasks so that your team can know the order in which they should start each task.

2 - Building a network

Now that your list is ready, it's time to build the network connecting them with arrows and circles.

The ➡️ arrows represent the tasks to be completed. They also indicate the flow and sequence to follow toward project completion. They connect two circles ⭕ that represent the steps. These circles are divided into three parts:

  • Top left: the earliest date the task can be delivered.
  • Top right: the latest date the task can be delivered.
  • Bottom half: the milestone marker.
Earlier Date - Latest Date - Milestone Marker

3 - Determine the dates as soon as possible

Step 3 and Step 4 are the most technical parts of creating a PERT chart.

Determining the earliest start dates means choosing the earliest possible time when you can start a task in your project.

Our tip 👉 It is necessary to take into account the different dependencies of your tasks in order to determine the earliest start day or time. For example, you can't start a task that is dependent on another task that is not completed.

This step simply consists of representing a deadline for each step. This representation is a way to establish a temporality in the project.

4 - Determine the latest dates

If step 3 allows you to know when to start a task, step 4 allows you to define the date and time when you hope to finish it.

This information is chosen by adding up all the durations of the previous dependent steps while taking into account the duration of the step you are trying to measure.

5 - Determine the free float of a task

The free float determines the leeway available for a task. That is, whether a task can be delayed and whether this will have an impact on the overall project.

Calculating this headroom is simple: the difference between the latest and earliest dates.

☝️ Sometimes tasks don't have a margin and exceeding their delivery date could have a negative impact on the entire project.

6 - Develop the critical path

Once you have created and completed your PERT chart, it is time to define the critical path of your project.

The critical path is the identification of the most important and necessary steps that will help you determine the minimum duration of your project. The tasks in these steps are dependent on each other. It refers to tasks that do not experience slack.

Gantt chart template to download

The PERT chart may seem incomplete on its own. It is in fact the first step towards building a Gantt chart. Thus, a perfectly executed PERT chart will naturally lead you to the construction of a Gantt chart.

There are several methods to make a Gantt chart. You can use dedicated software, websites or even make charts.

Appvizer offers you a unique and free template to download in Excel format.

Download your Gantt chart


The PERT chart: the door to the Gantt

The PERT chart is a great tool to improve your project time management. Like many processes, it is necessary to always re-evaluate your PERT chart and adapt it according to changes and evolutions (delays, technical problems).

Let us know in the comments if you are used to working with a PERT chart!

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