Difference between Gantt and PERT Charts

Gantt versus PERT Chart

Project managers frequently use Gantt and PERT (Project Estimation and Report Technique) charts to show the constituent tasks within a project. These two charts are the most popular project management charts. Gantt charts and PERT charts are both very useful project management tools for visually communicating project information. They are both used to schedule tasks, keep the project on schedule and ensure that the timeline is met in accordance with the original project plan.

Depending upon the duration or complexity of a project, the effort may be broken down into phases or iterations, and those then broken down into tasks within each phase or iteration. Both the Gantt and PERT chart would be broken down in a similar manner, potentially using a new chart for each phase, or connecting them to convey the entirety of the effort. Gantt charts have milestones at the completion of key deliverables, while PERT charts utilize review tasks or ‘dummy’ activities at the end of each phase, during which the deliverables of that phase would be validated or as placeholders indicating an intersection of subtasks into one deliverable.

Each tool, however, has their respective strengths and weaknesses. The fact that both of them are quite easy to produce using project management software adds to the confusion between the two project management charts.

A key difference between Gantt Charts and PERT charts is the manner in which flow is conveyed. A PERT chart is essentially a flowchart, or network diagram, while the Gantt chart is a bar chart with volume of time determining how big the bar will be. PERT charts focus on the sequence of tasks and their dependencies between one another while Gantt charts focus on the time required for each task.

PERT Advantages and Disadvantages

These types of project charts were created in order to work on large projects with a great deal of unknowns and a large number of dependencies. The PERT chart starts off with what’s called an initiation node that then splits off into a network of tasks. A PERT diagram could end up with parallel and interconnecting task networks. As a result, when there are many interlinked tasks within the project, a PERT chart can end up looking being fairly complicated, and might cause more confusion for those unfamiliar with them. Frequently, Gantt charts, with their familiar calendar-like presentation are used in conjunction with PERT diagrams to convey projected scheduled.

The PERT chart is an effective way to display complex projects. A project is made up of a group of tasks. The critical path can readily be identified on a PERT chart. The critical path is series of tasks through the project which require the greatest amount of time to complete. A project will take as long as it takes to achieve all of the tasks in the critical path. The non-critical paths, can consume all of their slack with delaying the project.

Advantages of PERT Charts

• PERT diagram’s Critical path conveys important activities which can cause the project to run over.
• Critical path on PERT chart allows focus of resources and effort to reduce risk.
• Allows visibility into possible extreme delivery dates using PERT estimation as a result of potential opportunities to be exploited or risks which to mitigate.
• Excellent for projects focusing on research or new technologies.
• Lets the project manager manage to the critical path.

Disadvantages of PERT Charts

• Can become confusing for the uninitiated or when projects have complex task relationships.
• If some activities take longer than expected, the critical path originally being managed to might end up being wrong. If other paths are near the critical path, they, too should be managed diligently to prevent project overruns.

Gantt Advantages and Disadvantages

Gantt charts emphasize the time it takes to complete tasks. The Gantt chart is a type of bar chart that illustrates a project schedule, focusing on task timing. A Gantt chart, with its calendar-like schedule, makes it very easy to show the timeline for a project. Each individual task is shown with a bar representing the duration of that task. Gantt charts show the beginning and ending dates of the project and roll-up tasks. They are useful for planning and scheduling projects since it is graphical representation of the duration of tasks against the progression of time.

However, when there are multiple dependencies lining up for a given milestone, the lines frequently intersect or overlay, making it nearly impossible to determine which tasks are the true predecessors. The original Gantt chart didn’t even have this means of conveying dependency. The connecting lines to do were introduced later as a convention to provide this crucial aspect of project planning. As such, Gantt charts don’t show dependencies very well for more complicated projects.

Gantt charts are quite suited for project which are clear-cut and won’t need constant rearrangement and adjustment as the project continues. The Gantt chart depicts the amount of time a given task should take and the required resources for each task. In doing so, the Gantt chart quite suited to assessing the status of the project. It’s quite easy to tell if a task is completed by the time it should be. The only issue with that would be large tasks, wherein it is difficult to tell an accurate percentage of completion, which is part of all project management, regardless of the tool used to convey the schedule.

Advantages of Gantt Charts

• Provide an excellent presentation tool for illustrating sequence of the task and demonstrating individual resources scheduled to time.
• A Gantt chart shows the steps by which tasks should be carried out.
• Easy to identify what should have been achieved at any point in the schedule.
• Makes it easy to ensure that the project is completed on time.
• Easy to prepare, manage, and present.
• Easy to show the importance of special checkpoints with milestones.
• Ability to set meeting points or reviews of the project.
• It is best used to show summary of the whole project to the top management as it does not show detail information for every activity.

Disadvantages of Gantt Charts

• Estimates must be completed before the chart can be drawn.
• Do not effectively convey task dependencies in more complex projects.
• It is difficult to show two sets of dates when using techniques such as earliest start date and latest start.
• It fails to show the critical and non-critical tasks.
• Changes to the schedule require a redrawing of the chart.
• Resource assignments are not easy to illustrate.
• Several scheduling possibilities cannot be shown in the same chart.
• It does not highlight Work Breakdown Structure (WBS) elements with the highest risk of failure or delay.

Summary of Differences between PERT and Gantt charts:

1. A PERT chart is essentially a flowchart, or network diagram, while the Gantt chart is a bar chart.
2. PERT charts focus on the sequence of tasks and their dependencies between one another while Gantt charts focus on the time required for each task.
3. Gantt charts handle sequence and duration, while PERT charts manage large and complex projects with variable duration tasks.
4. Gantt charts focus on the time required to complete a task; whereas a PERT chart focuses on relationships between the tasks.
5. Gantt charts are straightforward and are not made for projects which will experience change; while PERT charts are intricate and tolerate great deals of unknowns.

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