While the name might sound funny, a PERT chart can help you get some serious planning done. It was invented by the U.S. Navy back in the 1950s as a network chart to help visualize and complete the Polaris nuclear submarine project.
But there's a lot more to know about PERT charts if you plan on using them to complete your own projects. In this guide, we'll look at the following:
- What is a PERT chart?
- Gantt chart vs. PERT chart: What's the difference?
- Why do project managers use PERT charts?
- How to create a PERT chart
Ready? Here's how to use a PERT chart as a powerful project management tool. ⚡
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What is a PERT chart?
PERT is short for program evaluation and review technique. In addition to being a mouthful, it's also valuable for calculating the realistic amount of time needed to complete a project.
Visually, a PERT chart contains:
- Nodes that represent project milestones
- Arrows that represent tasks
Once nodes and arrows are interconnected, they show the relationship between each. It becomes easier to visualize what tasks lead to what milestones and the logical order of a project from there.
Now, you can probably imagine how complex PERT charts can get if you try to draw tasks and milestones by hand. This is where it's helpful to find the right tools—namely software—that help you streamline the PERT chart creation and management process. A PERT chart is of no use to you or your team members if it's filled with misleading arrows and nodes.
PERT charts use a three-point probabilistic estimate to calculate average task duration (the arrows). These estimates include:
🤞 The optimistic time estimate
🤝 The most likely time estimate
👎 The pessimistic time estimate
PERT charts use the following equation to find an average estimate: (O+4M+P)/6, where O is the optimistic estimate, M is the most likely estimate, and P is the pessimistic estimate.
The 4 represents the added weight given to the most likely estimate because, well, it's the one that's the most likely to happen. Once you divide by 6 to average these estimates, you get a number that tells you how much time a task will take on average with more accuracy.
Say you're an agency taking on a brand redesign project but you need to find out how long redesigning the website from scratch will take. Let's say these are your expected time estimates:
- The optimistic estimate: 20 hours
- The most likely estimate: 35 hours
- The pessimistic estimate: 53 hours
Once you plug your numbers into the PERT equation—(20+4(35)+53)/6—you get an average of 35.5 hours. From here, you're now able to allocate your time to the web redesign portion of the rebrand with more accuracy.
Gantt charts vs. PERT charts: What's the difference?
Though they have plenty of similarities, key differences set both Gantt charts and PERT charts in their own category. Both PERT and Gantt charts are used to manage projects. Where they differ is the type of information they provide for you to manage your project better.
While a Gantt chart helps:
- Anticipate how long it'll take to complete a task
- Keep teams aligned
- Visualize the flow of a project
...a PERT chart:
- Shows the dependencies of specific tasks
- Helps you determine the critical path to project completion
- Helps you break down and visualize projects that require more complexity
When in doubt, use both charts to get a clearer picture of the lifecycle of your project. Keep in mind that a PERT chart especially helps before beginning a project, so you can anticipate and plan for resources before diving in. 🙌
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Why do project managers use PERT charts?
When you bring PERT charts and project managers together, it's the perfect formula for getting a better handle on the scope of a project. With PERT charts, project managers are equipped to do things like:
- Visualize long, complex projects and break them down for the team
- Anticipate changes to available resources
- Plan around dependencies
- Estimate the time tasks will take
- Visualize parallel tasks that will happen simultaneously
- Know the minimum amount of time a project will take to complete
- Improve communication among stakeholders
It's easy to see how so many of the benefits of PERT charts can make for a better project lifecycle. It helps project managers stay within the three constraints of time, costs, and resources.
How to create a PERT chart
To get access to all the perks a PERT chart offers, you'll need to learn how to create one effectively.
1. Understand project scope and list project tasks
First, it's crucial to understand the scope of your project by creating a thorough list of project tasks—regardless of whether they're big or small. Listing project tasks will help you accurately map out dependencies as you build your chart and help you accurately identify a critical path.
Here's where a tool like Float can come in handy. You can add project timelines to track progress and key deadlines. It also makes it easy to set a project budget to forecast delivery and track spend in real time. But more on that later.
2. List tasks and their start date and end dates
Now you'll want to list tasks in chronological order and include what each of their deadlines is. For example, if you need X to complete Y, you'd list X as the first task and Y as the second.
Here's where you'll want to estimate task completion times with the PERT estimate equation—(O+4M+P)/6—to land on a more accurate estimation based on optimistic, most likely, and pessimistic outlooks.
Thankfully, you don't have to do all this with pen and paper. With Float, you can link task dependencies to visualize project workflows and make bulk changes. You can also designate deadlines and estimated time to complete.
3. Map dependencies
A dependency is when any single task or milestone depends on completing another task before the other task can be completed. Listing your tasks in logical order will make it easier for you to map dependencies. A PERT chart maps dependencies by numbering and connecting tasks.
Mapping dependencies can look like chronologically drawing diverging arrows (tasks) and connecting them to nodes (milestones). In the project phase below, the marketing tasks for the project cannot be worked on until the branding and recruitment tasks have been completed first.
So your PERT diagram would have the tasks of branding and recruitment come first, and it would then point to marketing as the task that would come next.
4. Draw your network diagram and visualize the PERT chart
As you draw and connect your dependencies, you have this step pretty much finished. You'll end up with a PERT chart that'll help give you a wider-lensed visual of what executing your project will look like. You'll also be able to identify bottlenecks in your flowchart that can throw off your entire project.
Looking through the dependencies and the critical path in your PERT chart will help find available resources for your project.
5. Find available resources
With a fresh PERT chart in hand, you can start looking for your available resources.
⏰ What are the available hours for your full-time, part-time, and contractor employees?
💸 What are the budget constraints on your hours?
🤹♀️ Who can apply certain skills to tasks without any slack time to shorten its specific time of completion?
This is also where you can start taking a closer look at each task on your PERT chart and finding where you'll have to allocate more resources—and even where you need to do additional project planning to optimize for efficiency.
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6. Identify a critical path
The visuals of a PERT chart make it easy to identify a critical path—or the path that takes the longest to complete. Once you identify a critical path, you'll want to take a closer look at each task on that path to see where you can decrease the time needed to complete that task, plan for efficiency, or estimate how long that task will take to be better prepared.
The critical path method helps optimize project execution and accounts for one of the project schedule's biggest constraints: time.
7. Tweak the chart as your project progresses
Building on the examples above, you'll start to create a fuller diagram of nodes representing milestones and tasks represented with arrows (which can be overwhelming when you start to map out an entire project's scope).
An easier approach is using a resource management tool with project planning features. You can tweak the chart as your project progresses and things like your project duration change. Maybe your team's availability isn't the same, so the time allocated to a task will differ. Or a deadline was missed last week, which sets your whole project back by two days.
Using a resource management software like Float makes project planning more precise and visual than traditional PERT charts. With features like linked tasks and milestones, you can break projects into manageable parts and move tasks together when a timeline changes.
This makes it easier to keep track of important dates and phases, so you can navigate any project constraints that arise.
PERT charts help you carry projects to completion
There's no doubt PERT charts can help evaluate the time and resources needed to complete a project. They allow you to break down complex projects, plan around dependencies, estimate how long tasks will take, and improve communication amongst stakeholders.
Creating PERT charts today is much easier when using a resource management tool like Float. You can get a birds-eye view of an entire project before it starts, avoiding potential bottlenecks.
Plus, you can visualize project priorities, shift related tasks when a timeline changes, and sequentially plan and schedule projects—all in one place! What's not to like about that?
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