12 Gantt Charts
Content for this chapter was adapted from Wikipedia, the free encyclopedia
Introduction
A Gantt chart is a type of bar chart that illustrates a project schedule. This chart lists the tasks to be performed on the vertical axis, and time intervals on the horizontal axis.The width of the horizontal bars in the graph shows the duration of each activity. Gantt charts illustrate the start and finish dates of the terminal elements and summary elements of a project. Terminal elements and summary elements constitute the work breakdown structure of the project. Modern Gantt charts also show the dependency relationships between activities. Gantt charts can be used to show current schedule status using percent-complete shadings and a vertical “TODAY” line as shown in the graphic above. There is not one correct way to create a Gantt chart, but the chart should include clear dates and separate major milestones in the project. Gantt charts represent a commitment to a timeline for the project by a team. This also means that creating a Gantt chart involves some estimation about how long each project will take and create a structure for the team to follow in order to reach their goals. Gantt charts are usually created initially using an early start time approach, where each task is scheduled to start immediately when its prerequisites are complete. This method maximizes the float time available for all tasks. Gantt charts are “one of the most widely used management tools for project scheduling and control” In the following table there are seven tasks, labeled a through g. Some tasks can be done concurrently (a and b) while others cannot be done until their predecessor task is complete (c and d cannot begin until a is complete; a dependency relationship). Additionally, each task has three time estimates: the optimistic time estimate (O), the most likely or normal time estimate (M), and the pessimistic time estimate (P). The expected time (TE) is estimated.
| Activity | Predecessor | Time estimates | Expected time (TE) | ||
|---|---|---|---|---|---|
| Opt. (O) | Normal (M) | Pess. (P) | |||
| a | — | 2 | 4 | 6 | 4.00 |
| b | — | 3 | 5 | 9 | 5.33 |
| c | a | 4 | 5 | 7 | 5.17 |
| d | a | 4 | 6 | 10 | 6.33 |
| e | b, c | 4 | 5 | 7 | 5.17 |
| f | d | 3 | 4 | 8 | 4.50 |
| g | e | 3 | 5 | 8 | 5.17 |
Once estimates and dependencies are understood, a team can draw a Gantt chart or a network diagram. Below are several examples of Gantt Charts.
A Gantt chart created using Microsoft Project (MSP). Note (1) the dependency relationships are in red, (2) the float time is represented by black lines connected to non-critical activities, (3) since Saturday and Sunday are not work days and are thus excluded from the schedule, some bars on the Gantt chart are longer if they cut through a weekend.
See this tutorial from Microsoft Office for a step-by-step guide to creating a Gantt chart in excel. If you’re reading the text version of this book, visit https://support.mic