The GANTT diagram is a tool that allows the user to model the planning of tasks necessary to the performance of a project. It is named after its inventor Henry Gantt who created it more than 100 years ago, in 1917. Given the relative ease of reading GANTT diagrams, this tool is used by almost all project managers in all sectors to control and manage the workflow, project stages, and progress representation in real time. Read on to know more about GANTT chart.
The GANTT diagram is a tool for the project manager, which allows for the graphic representation of the project's progress, but it is also a good means of communication amongst the various persons involved in a project. This type of modeling is particularly easy to implement with a simple spreadsheet (you can create GANTT charts in Excel, for example), but there are also specialized tools specially designed for project management, such as GANTT Project.
How to create a GANTT diagram?
In a GANTT diagram, each task is represented by a line, while the columns represent the days, weeks, or months of the schedule depending on the project's duration.
- The estimated time for a task is modeled by a horizontal axis, the left end of which is positioned on the intended start date and the right end of which is on the intended end date.
- Tasks can be placed in sequential chains or carried out simultaneously. If tasks are sequential, priorities can be modeled using an arrow from the upstream task to the downstream task.
- The downstream task cannot be carried out until the upstream task has been completed.
As a task progresses, the bar representing it is filled proportionally to its degree of completion. Thus, it is possible to get a quick overview of the project's progress by tracing a vertical line across the tasks at the level of the current date.
- The completed tasks are located to the left of this line;
- Tasks that have not yet begun are at the right, while the tasks being carried out are crossed by the line.
If their filling is located to the left of the line, the task is delayed compared to the plan.
Ideally, such a diagram should not have more than 15 or 20 tasks to fit on a single A4 page. If the number of tasks is more significant, it is possible to create additional diagrams detailing the planning of the main tasks.
What are milestones?
Additionally, it is possible to have significant events other than the tasks shown on the plan as points of connection for the project: these are the milestones.
The milestones allow the project to be decided in clearly identifiable phases, which avoids the end being too far off (this is often referred to as the "tunnel effect", a project with a long duration and no intermediate endpoint). A milestone could be the production of a document, the holding of a meeting, or a project deliverable. The milestones are tasks of zero duration, represented on the diagram by a specific symbol, most frequently a reverse triangle or a diamond.
It is generally possible (and useful) to show resources, human or material, on the diagram, to allow for estimation of needs and give an idea of global cost.
For the sake of concision, the initials or the names of those responsible for each task will sometimes suffice.