Posted by Philip Baskerville in Jun, 2015
Project Managers can use a range of tools and techniques to develop, monitor and control project schedules. Increasingly, many of these can be applied digitally (using programs such as Excel, Microsoft Project and so on).
GANTT Chart
This is a horizontal bar chart plotted over time (e.g. days, weeks or months). Each activity is shown as a bar (its length based on a time estimate). Depending on task dependencies and resource availability, these bars may be sequential, or run in parallel. Each bar is plotted to start at the earlier possible start date. The plan laid out when the GANTT Chart was created can be compared with actual times taken (plotted below the planned time bars in the chart).
Schedule Network Analysis
The schedule network is a graphical display (from left to right across a page) of all logical interrelationships between elements of work — in chronological order, from initial planning through to project closure. As a project progresses, regular analysis of this network diagram is a check to ensure the project is proceeding ‘on track’.
Critical Path Method
The critical path of a project is the sequential string of activities that takes the longest time to complete, recognising any dependencies between tasks in this sequence (e.g. one cannot start till another finishes). Arrowed lines represent activities with circles at each end representing milestones (start and finish).
The critical path method (CPM) determines by adding the times of all activities on the critical path, the earliest time that the project can be completed
Non-critical activities have an earliest and latest start time (ES and LS, respectively) and an earliest and latest finish time (EF and LF, respectively). The ES and EF are found by working forwards through the project network and the LS and LF by working backwards. The difference between the LF and EF of each activity have zero float; they must be done when planned or the project overall will be delayed.
PERT (Program Evaluation and Review Technique)
PERT charts differ from CPM charts in the way times are calculated for activities. They allow better for uncertainty. For each activity, three estimates of time are obtained: the shortest time (SP), the longest time (LT) and the most likely time (MT). The estimate assigned for the activity is a weighted average of these three estimates. The formula is:
Expected time = (SP + 4(MT) + LT) /6.
Schedule Compression
A schedule can be shortened two ways: • crashing: using more resources than planned on the task
• fast-tracking: adjusting the schedule so, mindful of task dependencies, more activities are done in parallel than was planned
Risk multipliers
This involves building in a time or resource contingency for tasks considered to be at high risk of overrun.
Resource tools and techniques
• Levelling: This involves adjusting the activities within the schedule so as to ensure there are minimal peaks and troughs in resource use. This ensures efficient use of resources. It also allows the Project Manager to direct resources, where required, to more critical activities. • Critical chain method: Activities are planned in the light of their latest possible start and finish dates. The extra time that results between some activities can be used to better use resources.
• Resource histograms: This is a column chart that depicts the resources used on a project over time.
Additional resources
For more information on scheduling tools and techniques, view: <//www.acornlive.com/demos/pdf/E2_EM_Chapter_7.pdf>. For more information on preparing a GANTT Chart, view:
<//www.youtube.com/watch?v=CZ38xTLRAjo>.
For more information on the basics of using Microsoft Project, view:
<//www.youtube.com/watch?v=sPwURRG9_Gs>.
Smartsheet Contributor Diana Ramos
February 25, 2021
Gantt charts and PERT charts are popular project management tools. In this article, we explain their differences and similarities, as well as when to use them. Plus, you can learn their connection to the critical path method.
Included on this page, you can find a comparison of the two types of chart, how to decide which works best for your needs, and an example project represented in both PERT and Gantt charts.
PERT and Gantt charts enable project managers to track tasks and project status. PERT charts display tasks in a network diagram, highlighting dependencies; Gantt charts show tasks and timelines in a bar graph. Both have a place in the PMBOK’s work breakdown structure (WBS).
PERT (Program Evaluation and Review Technique) charts are often part of planning, and project managers use them before the start of a project to determine the anticipated length of each task. Here’s how organizations can use a PERT chart for projects:
- The project manager and team define all activities and tasks necessary to complete a project, estimate the time to complete each task, and develop a preliminary time frame.
- In a network diagram, each task is in a separate box that shows its dependencies in relation to other tasks.
- A PERT chart doesn’t have an x- or a y-axis, but each box shows the start and completion times for its task.
Read our guide to PERT charts to learn about their origin, common terms, and ways to use them effectively.
Organizations generally use Gantt charts for tracking the status of tasks and highlighting scheduling constraints. Project managers might also use them before a project to break down tasks into smaller tasks. Here are some characteristics of a Gantt chart:
- Tasks appear in a linear fashion on a bar chart.
- The layout makes it easy to see the expected duration of each task and the entire project.
- Gantt charts are also useful for coordinating resources and scheduling team members.
- When you look at a Gantt chart, the x-axis shows the timeline, and the y-axis displays the tasks.
Read our article on Gantt charts to learn more about their history, benefits, and use cases. You can also learn how to create a Gantt chart or download Gantt chart templates and other WBS-related templates.
| Development | Created by Henry Gantt in the early 1900s so people could see a project’s status at a glance. | Developed by the U.S. Navy in the 1950s to help manage complex projects. |
| Description | A bar chart that shows the status and dependencies of tasks in a project. | A network diagram that illustrates the status and dependencies of tasks in a project. |
| Data Included | Project duration, dependencies, project phases, and responsibility. | Project duration, dependencies, critical path, and responsibility. |
| Usefulness | Used to track the status of each task and break tasks into smaller segments while a project is in progress. | After defining tasks, use the chart to create a timeline for the project. |
| Alterations | The original form of the chart didn’t show dependencies; they have been added in newer versions. | Some versions of the chart are basic and only show the task; others can contain more information about each task, such as the responsible party and completion percentage. |
| Format of Presentation | Bar chart, where each bar represents a task. | Network diagram with boxes that represent tasks. |
| Time Structure | The x-axis is the project timeline. | There is no axis to represent time. |
| Critical & Non-Critical Path | Critical path can’t be easily found when using Gantt charts. | Critical path can be easily found when using PERT charts. |
| Percentage of Task Completed | A filled-in bar represents a task and shows the completion percentage. | There is space to add the completion percentage in the box representing the task. |
| Relationship Between Tasks | In some versions, lines connect dependent tasks. | Arrows connect dependent tasks. |
| Reading the Charts | Generally read left to right to track the status of tasks and sometimes to track the critical path. | Generally read holistically to trace the critical path and, in some cases, to track the status of projects. |
| Prediction of Task Completion | The most common form of the chart fills in the bar to represent the completeness of a task, so it’s easy to visualize. | Many versions of the chart have a field for completion percentage, but it isn’t always easy to read. |
| How the Chart Relates to WBS | Generally used in the execution stages. | Generally used in the planning stages. |
PERT and Gantt charts have some commonalities. You can use them to chart the same activities, but they differ in appearance.
A Gantt chart is a bar chart with the x-axis and y-axis representing tasks in a timeline.
A PERT chart is a flow chart or network diagram that displays project tasks in boxes and links them with arrows that outline dependencies.
PERT charts are network diagrams, so they are useful for showing dependencies between tasks. They have three options for activity duration: Most Likely, Optimistic, and Pessimistic. PERT charts are a more flexible planning tool than Gantt charts.
A Gantt chart shines at monitoring the status of tasks. It might take some work to create one (though software solutions greatly reduce the load), but they’re well worth the effort for the following reasons:
- Gantt charts generally aren’t as complicated as PERT charts and are usually easier to read.
- Project managers can adjust the tasks in a Gantt chart as the project progresses. This real-time view of progress keeps the team on track for timely delivery, improves efficiency, and optimizes time management.
- Tracking the order of tasks and completed tasks is easier with a Gantt chart.
- Gantt charts are better than PERT charts for monitoring a project status.
Here are some tips to help you choose between a PERT chart and a Gantt chart, depending on your goals:
- Use a PERT chart when you need to:
- Anticipate the amount of time it takes to complete the project
- Determine the critical path to meet your deadlines
- Plan for large or more complex projects
- Show the interdependence of tasks
- Use a Gantt chart when you need to:
- Anticipate the amount of time to complete each task
- Clearly communicate task responsibilities
- Communicate the project’s progress
PERT and Gantt charts highlight different aspects of tasks in a project. Here are examples of each chart type covering the same tasks in a project. In this case, these sample charts look at the first steps in building a house.
You can see the differences between the two charts below. Compare the information displayed in each and the variations in how the charts present the same information.
You might be able to convert a Gantt chart to a PERT chart in Microsoft Project by changing the data display. Microsoft Project does most of the work when you switch the view to Network Diagram. If not, try this:
- Open an existing Gantt chart and a blank PERT chart.
- Add a new task to the PERT chart.
- Copy and paste key data, like start date, end date, person responsible, and percent complete from the Gantt chart to the PERT chart. Repeat for each task.
- If you have dependency lines between related tasks, copy them from the Gantt chart to the PERT chart. If you don’t, create them. Repeat for each task.
You’re done. Admire your new PERT chart.
PERT charts and Gantt charts can be used to track the critical path of a project. But since part of the critical path method (CPM) involves estimating the completion time by the best, most likely, and worst-case options, the PERT chart is a better option.
The critical path method (CPM) is a project management technique in which you add all tasks for a project and their dependencies to a chart. Then you calculate the project duration based on estimated durations for each task and the associated dependencies. Once you add all tasks and dependencies to the chart, you can uncover the critical path by tracing the tasks and dependencies.
The critical path is the longest sequence of tasks in a project plan that, when you finish each on time, enables the project to be completed on schedule. A delay in any task on the critical path pushes back the timeline for the entire project. Most projects have a single critical path, but some projects have multiple critical paths. Read more about the critical path method.
Empower your people to go above and beyond with a flexible platform designed to match the needs of your team — and adapt as those needs change.
The Smartsheet platform makes it easy to plan, capture, manage, and report on work from anywhere, helping your team be more effective and get more done. Report on key metrics and get real-time visibility into work as it happens with roll-up reports, dashboards, and automated workflows built to keep your team connected and informed.
When teams have clarity into the work getting done, there’s no telling how much more they can accomplish in the same amount of time. Try Smartsheet for free, today.
Try Smartsheet for Free Get a Free Smartsheet Demo