- What Is PERT?
- What Is the Difference Between PERT and CPM?
- Why Use a PERT Chart?
- Pitfalls of PERT
- What Is PERT Chart Software?
- Benefits of PERT Chart Software
- Must-Have Features of PERT Chart Software
- PERT Charts in Project Management
- Steps to Creating a PERT Chart
- How to Calculate PERT
- How to use the PERT Formula
- PERT Chart Example
- PERT Chart Video
- PERT Chart Resources
What Is PERT?
PERT, or the Program Evaluation and Review Technique, is used by project managers to create realistic schedules by coordinating activities and estimating time durations.
The Program Evaluation and Review Technique allows project managers to assign three time estimates (optimistic, most likely and pessimistic) for each project activity. This makes PERT a perfect choice for planning projects where activity times are uncertain.
What Is a PERT Chart?
A PERT chart is a statistical tool used in project management that analyzes and tracks activities and milestones by mapping them out on a timeline.
A PERT chart is event-oriented: it’s comprised of numbered nodes, directional arrows and divergent arrows that illustrate the minimum time and duration of activities. Activities are represented by these arrows, and nodes are the milestones associated with them.
The raw data produced by PERT can be imported into project scheduling software, which helps you manage the whole project. You can use a Gantt chart to create a practical schedule, manage your resources and deliver on time and under budget.
ProjectManager.com makes harnessing your PERT chart simple. Sign up for a free trial today and make dynamic project schedules that update in real time as your team completes their tasks.
What Is the Difference Between PERT and CPM?
PERT and the Critical Path Method (CPM) both make use of network diagrams to estimate the duration of individual activities and projects, but they’re different. For instance, the PERT diagram represents activities as arrows and milestones as nodes. While, on the other hand, the CPM diagram depicts activities as nodes.
Also, PERT offers the possibility of including three time estimates for activities (optimistic, most likely and pessimistic) which is not possible with CPM. This is because PERT was designed to plan projects with uncertain activity times, while CPM is used for projects where activity times are known.
Using CPM & PERT in Project Management
PERT is often used along with the critical path method (CPM), which is a network analysis that discerns which tasks and activities must be completed to deliver a successful project. They’re used together when planning costs, scheduling resources and controlling a project to keep it on schedule. When combined, they result in a more conservative view of the duration of tasks and activities.
While the PERT asks for the most likely, the optimistic and pessimistic durations of a task, the CPM asks similar questions—only phrased slightly differently. CPM uses a single time estimate for each task and focuses on the analysis of the duration task sequences to estimate the total time required to complete a project.
CPM allows project managers to identify the critical activities of a project, which are those that can’t be delayed. Using them together within a project management software results in a more complete analysis of the project plan and a more accurate timeline.
Why Use a PERT Chart?
The PERT chart is used to estimate the minimum amount of time that will be needed to close a project. This is done by examining the breakdown of the project, estimating the duration of each activity, the dependencies between them and the order in which they must be completed.
Simplify Complex Projects
PERT charts help project managers get a handle on complex projects. They’re useful because they provide an estimation of how much time you’ll need to schedule the project and what resources will be required. The nature of the PERT chart and its breakdown structure helps to visualize the complexity of a project and the dependencies between each step in the process.
Involve Multiple Departments & Subject Matter Experts
A PERT chart also serves as an organizational tool that pulls in data from every department working on the project. This helps identify who is doing what, and provides clear responsibilities for those tasks. Strong communication is facilitated between departments, and the overall strategic goals of the organization are better aligned.
Explore the Hypothetical
Another benefit of using a PERT is it allows you to create what-if scenarios. By mapping out the time and resources for a project, you can quickly see what is working and what is not. This saves a lot of time that would otherwise be wasted in revisions. This flexibility makes PERT useful in project management.
Pitfalls of PERT
PERT charts are not a panacea to get your projects magically on track, though. Naturally, bad data-in will result in bad data-out. It’s important that the person creating the PERT has experience in the process.
They’re also labor intensive, which some organizations might not have the time or money to invest in. Additionally, you just don’t build a PERT and call it a day. They require continuous reviews and updates to make sure they’re accurate.
What Is PERT Chart Software?
PERT chart software is used to help managers better estimate the realistic duration of their project. PERT charts are a form of diagram, and can be built robustly using a dedicated PERT chart tool.
PERT chart software is really a feature of a larger project management tool that takes the diagram and imports it into a Gantt chart. Now, the PERT can be the stepping stone to adding durations to your tasks, linking dependencies, setting milestones and assigning work to the team. Microsoft Project is one of the most commonly used project management software, but it has major drawbacks that make ProjectManager.com a better choice.
Benefits of PERT Chart Software
PERT chart software, combined with a fully loaded project management software, is the ideal tool to manage projects from initiation to closure. You now have features that organize your tasks to schedule and assign them to teams, as well as monitor and control the tasks as they are executed.
The benefits of having software that can take the PERT chart and tie it to the overall project are many. Here are just a few:
Organize and Schedule Tasks
PERT charts give you an idea of how long the project should take, and a Gantt chart fine tunes that by collecting all your tasks on a project timeline. Estimate the duration of each task, set milestones to better track as you move from one phase to another and assign your team work.
Link Tasks, Avoid Bottlenecks
Gantt charts control tasks by linking dependent ones together. Some tasks can’t start or finish until another starts or finishes. If you don’t identify these during the planning stage, you might block the team when they’re executing their work. Linking dependencies keep you on track.
Plan Your Project Timeline
Gantt charts are a manager’s go-to tool for scheduling projects. They manage all your tasks, subtasks, resource costs associated with the tasks and even planned starts and finishes. Then, by setting a baseline, you save that data and can compare it against your actual progress.
The critical path is an algorithm that is used to better schedule projects. The calculation is somewhat complex, and pulls you away from other important project duties. Some Gantt charts will automatically chart the critical path in your project, which saves time.
See Project Metrics in Real-Time
Dashboards are a collection of project metrics displayed in graphs and charts that give you a bird’s-eye view of the project’s performance. If you’re using online software, that data is delivered in real-time to give you a more accurate status report on progress.
Make Data-Driven Decisions
The PERT chart estimates, project reporting defines. Reports can be generated to show project variance, task and time progress, workload, costs and more. They provide accurate data to make better decisions and can be shared to keep your stakeholders updated.
PERT Charts in Project Management
As stated, the use of the PERT chart gives project managers a tool to estimate the time and resources needed to complete their project, which is crucial during the initiation and planning phases.
When it comes to starting a project, the early steps involve taking all those tasks you collected that lead to your final deliverable and organizing them in a schedule. Knowing the amount of time it’ll take to complete each task, especially the riskier ones, is fundamental to creating a viable schedule.
What Is the Difference Between a Gantt Chart and a PERT Chart?
While both PERT charts and Gantt charts are visual tools used by project managers to control tasks scheduling, they are not exactly the same thing.
PERT charts, as detailed above, were developed to simplify planning and scheduling larger and complex projects. A Gantt chart, on the other hand, is also a graphical depiction for planning and scheduling a project, which breaks down the project scope into tasks that populate a timeline. A Gantt chart can be used to build the project timeline, set task dependencies and show the duration of each task.
There are other key differences, as well. For example, in a Gantt, the timeline is represented by a bar chart. A PERT chart is more of a flowchart or network diagram. Gantts can be used on smaller projects, while PERT charts are for larger and more complex projects. Dependent tasks are linked on a Gantt, while a PERT has many interconnecting networks of independent tasks.
The most salient difference is that a PERT chart is usually used before starting a project to figure out scheduling, while Gantt charts tend to follow into the project, highlighting scheduling constraints. Gantt chart software can be used when executing the project as well as when planning because a task’s start and end dates can be edited. Gantt charts reveal how long each task will take, show who on the team is responsible for those tasks and generally are a more transparent tool to track progress.
Pro Tip: A PERT chart is a great way to help you estimate simply and more accurately. Estimates can be overly optimistic or pessimistic, but using a PERT chart will find the most realistic estimate.
Steps to Creating a PERT Chart
Use a PERT in the planning phase of your project. Here are the steps in broad strokes:
- Begin by identifying the project milestones and then break those down into individual tasks.
- Figure out the sequence of the tasks.
- Make the PERT diagram — we’ll show you how in the section below!
- Do an estimate for each task and the time it will take to complete it.
- Calculate the critical path and identify any possible slack.
- You have your PERT chart! Remember, the PERT chart is a living document that must be returned to and revised as needed as the project progresses.
How to Calculate PERT
Before we create a PERT chart, it’s helpful to know how to calculate PERT itself.
PERT relies on the weighted average of three numbers that are based on the most pessimistic (P), the most optimistic (O) and the most likey (M) estimates for the project’s length.
- Optimistic Time: The least amount of time to accomplish a task or activity. This is a scenario when everything is working and you beat the estimated schedule.
- Pessimistic Time: The maximum amount of time to accomplish a task or activity. This is the worst-case scenario, anything that can go wrong does.
- Most Likely Time: The best estimate of how long it will take to accomplish the task or activity, assuming there are no problems. This would be your estimation working out perfectly, as rare as that might occur.
- Expected Time: The best estimate of how long it will take to accomplish the task or activity, assuming there will be problems. This would be the more realistic duration.
Using the figures you come up with for P, O and M, calculate the equation:
How to Use the PERT Formula
Using the optimistic, most likely, and pessimistic time estimates, you can use the PERT formula to calculate the expected duration of a task:
(O + (4*M) + P) / 6
The result is a weighted average, which is an average from multiplying each element by a factor that reflects its importance. You can think of this as the expected time, though often the calculation will bend towards the pessimistic. That’s because usually the pessimistic figure is larger than that of the optimistic one.
This calculation helps you estimate all the tasks in your schedule, but it can also focus solely on activities that are high risk. The latter is helpful as the more risky the task, the wider the margin of error is when making an estimation of how much time it’ll take.
What Is the Standard Deviation in PERT?
To determine the standard deviation of the estimate of an activity, subtract the pessimistic number from the optimistic one and divide the results by six. The larger your results, the less confidence you have in your estimate, and vice versa; the smaller the figure, the greater your sense of confidence in the estimation. The PERT standard deviation formula is shown below:
(P-O) / 6
PERT Chart Example
Let’s move these concepts from abstraction to reality. To better understand the power of a PERT chart, let’s make one together. For our PERT chart example, we’ll create a project around building a website. The PERT chart will allow us to visualize our project’s activities and milestones to quickly uncover the critical path.
Observe the PERT Chart below, and we’ll walk through how we created it.
To begin, we’re going to identify all the activities that make up the project and determine the immediate predecessors for each. We’ll list them as shown in the table above, known as the activity list. Milestones are not included because they’re the outcome of each activity.
Next, we figure out how long all the activities to get to our milestones will take. The amount of time you estimate with the PERT formula should be added to each vector as shown in our example chart. We used weeks as our time unit, but it could be days or months, depending on your project.
Once we have a time estimate for each task, we can draw our network diagram. We start with the first node which is the “kick off meeting” in our example. Then we represent the initial activities with vectors and connect them to their corresponding milestones. We continue the process until we get to the final milestone of our project.
With the completed chart, it becomes clear which activities are critical to delivering the project on time. These are represented by the white vectors. Once the critical path is determined, you can easily refer to it to keep your project on track!
Glossary of Terms Related to PERT Charts
These concepts will allow you to understand the Program Evaluation and Review Technique and the anatomy of a PERT chart:
- Nodes: These are the symbols used to visualize milestones and project tasks. They can be represented by circles or triangles.
- Vectors: Visual representation of the sequence of a task, diverging arrows indicate tasks that can be completed at the same time. They can be solid or dotted, depending on the nature of the sequence.
- PERT Event: The start or end of a task.
- Slack: The amount of time a task can be delayed without causing an overall delay to the project or other tasks, also known as float.
- Critical Path: Charts the longest path from beginning to the end of a task or event.
- Critical Path Activity: An activity with no slack.
- Lead Time: How much time you should complete a task or activity without impacting the following ones.
- Lag Time: The earliest time in which a task can follow another.
- Fast Tracking: Working tasks or activities at the same time.
- Crashing Critical Path: Shortening the time of a task. This is the longest path from the starting milestone to the finish. If you experience a delay on the critical path, it will impact the entire project.
- Predecessor: An activity that precedes another, and must finish before its successor can start.
PERT Chart Video
All of these explanations can be a bit hard to understand by text. If you’re more of a visual learner, watch project management expert Jennifer Bridges, PMP, as she walks you through the steps of creating a PERT chart in this short tutorial video.
History of PERT Charts
PERT in project management has been around for a while, but it was, in fact, developed by the U.S. Navy. In 1957, the Special Projects Office created the PERT chart to assist in its Polaris nuclear submarine project.
Since then, the Program Evaluation and Review Technique found a home in all manner of industries and even in the 1968 Winter Olympics in Grenoble.
PERT diagrams and the critical path method came about at roughly the same time, growing from the scientific management founded by Frederick Taylor, also called Taylorism, which was later refined by Henry Ford. But the use of the term critical path comes from DuPont, which developed the method also in the late 1950s.
Moving Beyond PERT with ProjectManager.com
The PERT chart is a tool that helps plan and schedule. ProjectManager.com helps you take that PERT chart and apply it to managing your whole project with our online Gantt chart. It plans, schedules and works through the execution of the project. Our Gantt gives you control over every aspect of your schedule, from placing milestones, assigning team members and linking dependencies.
We easily link all four types of task dependencies — finish-to-start, finish-to-finish, start-to-finish and start-to-finish — so you can avoid bottlenecks later in the project.
Unlike a PERT chart, our Gantt isn’t static. No matter how good your estimations, there will always be issues that pop up in a project. You can prepare for risk and mitigate it, but often the schedule will have to adapt to keep you on time. We have drag-and-drop editing to quickly and easily change start and due dates, which is then reflected throughout the software.
That’s just the tip of the iceberg for our award-winning project management software. We can help you keep your projects and teams organized. See for yourself why tens of thousands of teams use our software to work more productively by starting your free 30-day trial.
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