PERT Diagram: Definition, Advantages and Examples

1. What is a PERT diagram?
2. What is a PERT diagram suitable for?
3. What are the benefits of a PERT diagram?
4. How do you create a PERT diagram?
5. Examples of a PERT diagram
6. When is a PERT diagram useful?
7. What are the differences between a PERT diagram and a Gantt diagram?
8. What project management tools are suitable?
9. Conclusion: Your guide in project management

Successful project management has to overcome many hurdles. Clever planning and effective visualisation of complex processes and relationships are important prerequisites. In this blog post, we explain a particularly powerful project management tool that solves exactly these challenges: the PERT diagram. And off we go!

What is a PERT diagram?

PERT stands for Program Evaluation and Review Technique and describes a method for planning and controlling projects in the form of a network plan. Within this method, the PERT diagram is used as a graphical tool. It defines the timing of a project, the dependencies between activities and enables the identification of the critical path.

Special symbols and arrows are used for creation to represent activities, milestones and dependencies between tasks. Basic elements of the PERT diagram include:

• Activities (Nodes): The various tasks in the project are represented by nodes.
• Arrows: Indicate the dependencies between the activities. They indicate which activity must take place before or after another.
• Estimates: Each activity is provided with estimated times for its completion.
• Events : Milestones or points where several activities come together or diverge.
• Critical path: The longest path through the network, which determines the shortest time for project completion.

Source: https://www.gliffy.com/blog/pert-chart

What is a PERT diagram suitable for?

As a project manager, your core task is to plan, monitor and control a project efficiently. With the help of the PERT diagram, you can visually display the project schedule, focus on milestones and particularly critical activities, monitor and control them. For your team, the PERT diagram also acts as an important basis for communication and helps them recognise activities and dependencies.

The PERT diagram is especially suitable for complex projects, ensuring a comprehensive insight into the timing and complex relationships within the project.

What are the benefits of a PERT diagram?

The PERT diagram offers several advantages within project management. Here are the most important ones: 

Visualisation of dependencies

PERT diagrams enable a clear visualisation of the dependencies between different tasks and activities in the project. This facilitates understanding of the order in which activities must be carried out.

Critical path identification

An important advantage of PERT diagrams is that they show the critical path in the project. This is the sequence of activities that determines the longest duration in the project. By focusing on the critical path, you can identify bottlenecks and concentrate on minimising delays.

Effective time management

PERT diagrams support time management by presenting the project schedule in clearly defined activities and their temporal dependencies. This helps you plan and allocate resources.

Risk management

By identifying dependencies and estimating activity times, the diagram uncovers potential risks. In this way, you can better respond to uncertainties and unforeseen events.

Clear communication

PERT diagrams provide a clear and easily understandable representation of the project plan. This simplifies overall project communication and thus improves team collaboration and cooperation with stakeholders.

Resource optimisation

By elucidating the temporal requirements and dependencies between activities, the diagrams ensure efficient management of your resources.

Project monitoring and control

PERT diagrams serve as a reference point for monitoring project progress. If you need to make updates, their impact on status and schedule will become immediately apparent.

What are the challenges with a PERT diagram?

Every tool has its limits, and PERT diagrams also have some pitfalls. For instance, the accuracy of a PERT diagram depends heavily on the quality of the estimates for the activity times. As a project manager, you therefore need to provide as realistic time estimates as possible. Incorrectly estimated times lead to a distorted schedule that does not meet the actual requirements of the project. The difficulty lies in adequately assessing uncertainties and unforeseeable events.

The complexity of PERT diagrams is often underestimated in practice. This applies especially to extensive projects and to people who are not familiar with the method. The multitude of activities, dependencies and events can make the diagram potentially confusing, which in turn can lead to misunderstandings and difficulties in interpretation. Therefore, it's important to train team members and stakeholders with regard to the meaning of the various elements in the PERT model. This ensures that all participants can effectively utilise the tool.

How do you create a PERT diagram?

1. Identification of activities

To create a PERT diagram, start by identifying all activities and tasks required for the project. Initially, enter them into a list or use directly a Project management software like awork, which supports you in all steps.

Make sure to formulate the tasks as clearly and precisely as possible to avoid confusion. For this step, understanding the project structure is usually helpful:

a) Main goal of the project: What is the overarching goal of the project? Understand the overall vision and define clear steps to achieve this goal.

b) Subtasks for goal fulfilment: Which subtasks need to be completed to achieve the main goal?

It is crucial to clarify the specific steps and dependencies between the activities. Consult experts and involve your team to gain as comprehensive knowledge as possible. Another option is to uncover ideas and potential activities through brainstorming. Invite your team to collect diverse perspectives. This participatory approach not only promotes the identification of activities but also strengthens engagement and collaboration within the team.

2. Determination of dependencies

It is now your responsibility to analyse the dependencies between the different activities. Find out which activities must be completed before others and in which order the activities must be carried out. Again, it is useful to integrate your team and conduct conversations and workshops with experts or stakeholders.

It is also important to prioritize the identified dependencies according to their critical importance for the project. This will help you to focus on the essential relationships, and to consider them appropriately in the planning. The inclusion of different perspectives and systematic prioritisation will certainly help you gain a clear overview of the sequence of activities and identify potential bottlenecks early on.

3. Estimation of activity durations

Before you move to the graphical representation, it is important to estimate the time that each activity will likely take. Use historical data or experiences from other projects to get as accurate values as possible. If there are activities that you cannot estimate accurately, plan in a buffer.

In practice, the following calculation is also proven to determine the expected time. For each activity, you define the following times:

1. Optimistic duration: Estimated time for the activity if everything goes ideally.
2. Pessimistic duration: Estimated time for the activity if unexpected difficulties or delays occur.
3. Likely duration: Estimated time for the activity under normal conditions.

Once you have estimated three values (optimistic, pessimistic, likely), calculate the expected duration. The formula is: 

Optimistic duration + (4 x Likely duration) + Pessimistic duration / 6

so: (O + (4 x W) + P ) / 6

Here is an example calculation: 

Optimistic time to complete a task (O): 100 minutes

Pessimistic time to complete a task (P): 160 minutes

Likely time to complete a task (W): 130 minutes

= (100 + (4 x 130) + 160) / 6 = 130

Expected duration: 130 minutes

4. Creation of the network plan

Now it's time to graphically record activities and dependencies. Use arrows to connect the activities and nodes to represent the events. An event is a point in the project plan where several activities come together or diverge.

Here are a few more tips:

• Use clear symbols for activities, events and arrows to make the diagram understandable for everyone.
• Number each activity uniquely to avoid confusion.
• Make sure the arrows correctly display the direction of the activities. An arrow should always point from the predecessor activity to the successor activity to clarify the logical order of the activities.
• If there are parallel activities in the project, represent them by branches in the network plan.
• Use colours to highlight different types of activities or specific events.
• Start and end points of the project should be clearly marked in the network plan, either by distinctive symbols or highlights.
• Mark milestones and interim objectives to monitor progress better.

5. Determination of the critical path

In the next step, you need to identify the path with the longest chain of interconnected activities necessary to complete the project. This path is referred to as the critical path. It includes activities that you should always keep an eye on.

In case of delays, it is crucial to act quickly in order not to jeopardise your schedule. Therefore, consider possible measures that could be necessary. Expanded resources or a more precise identification of activities that can occur in parallel are possible approaches.

By using simulation techniques and scenario analyses, you can test the effects of changes on the critical path before you implement them. This allows you to make informed decisions and choose the best strategy for maintaining the project schedule.

6. Review and update

Check the PERT diagram regularly to ensure it matches the current project conditions. Update it as needed, especially when activity durations change or new requirements arise.

Examples of a PERT diagram

PERT models are usually created with the help of Project Software . These tools offer practical templates, features like automatic calculation of the critical path and easy update options. The following screenshots show you templates and examples of PERT diagrams as displayed by project software:

Source: https://miro.com/templates/PERT-diagram/

Source: https://venngage.com/templates/diagrams/dark-simple-editable-PERT-chart-diagram-example-b6fb7266-7ea6-4a94-b021-1f2e9f45e652

Source: https://www.mindmanager.com/features/PERT-chart/

Source: https://creately.com/diagram/example/2j0JttvLWyK/pert-chart-example

When is a PERT diagram useful?

A PERT diagram is particularly useful when:

• You want to plan and manage complex structures, dependencies of activities and their duration purposefully.
• You are planning a project that has certain uncertainties and risks regarding schedules and activity durations.
• Monitoring and identifying the critical path is particularly important to you.

What are the differences between a PERT diagram and a Gantt diagram?

PERT diagrams and Gantt charts are two different approaches to visualising and planning projects. In many cases, PERT diagrams and Gantt charts are also used in combination to get a comprehensive overview of projects. PERT is particularly useful in projects with high uncertainty, while Gantt charts are often preferred for a clear temporal representation and communication with team members and stakeholders.

Source: https://www.officetimeline.com/blog/gantt-chart-versus-other-charts

What project management tools are suitable?

On OMR Reviews you find the best Project Management Tools at your disposal. We show you which functions these systems offer besides PERT diagrams and what costs you should expect. Particularly practical for the start are the free basic versions that many of the providers offer.

With these systems you manage your project tasks effortlessly:

Asana

awork

Trello

monday.com

Stackfield

Jira

Notion

Conclusion: Your guide in project management

The PERT diagram is a valuable method in project management to effectively plan, monitor and control complex projects. With the visualisation of activities, dependencies and the calculation of the critical path, the PERT diagram offers a comprehensive insight into the timing of a project. The emphasis on logical dependencies and the consideration of uncertainties in activity durations, makes it particularly suitable for projects with high complexity and uncertainty. If you as a project manager want to focus on the critical path, identify bottlenecks and efficiently react to changes in the project progress, use the PERT diagram as part of a full-featured and popular project management tool like awork. This brings the overall efficiency and success of the project a big step closer.