Gantt Chart

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The special type of horizontal bar chart that provides a graphical overview and schedule of all activities, elements and dependencies of a project or program. Explanation of the Gantt Chart of Henry Laurence Gantt. (1917)

Contributed by: Peter Darwin

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Gantt ChartWhat is a Gantt Chart? Description

The Gantt Chart from Henry Laurence Gantt provides a graphical overview and schedule of all activities, elements and dependencies of a project or program. It is a special type of horizontal bar chart that is very common in project management to represent the phases and activities of a project Work Breakdown Structure.


A Gantt chart is constructed with a horizontal axis representing the total time span of the project, broken down into increments (for example, days, weeks, or months) and a vertical axis representing the tasks that make up the project. Horizontal bars of varying lengths represent the sequences, timing, and time span for each task.


They may be simple versions created on graph paper or more complex automated versions created using project management applications such as Microsoft Project or Excel.


Optional Gantt Chart Enhancements

The progression of each activity can be shown by shading the bar as progress is made. Some Gantt charts also illustrate the dependency relationships between activities by using link lines or color codes. Milestones can be shown. Current schedule status can be shown by a vertical marker, the TODAY-line.
 

Origin of the Gantt Chart. History

Henry Laurence Gantt, A.B., M.E. (1861-23 November 1919) was a mechanical engineer and management consultant who is most famous for developing the Gantt chart in 1917, besides a number of others charts. The first Gantt charts were employed on major infrastructure projects including the Hoover Dam. Modern spreadsheet and project software enable the creation and editing of very comprehensive Gantt charts.


Usage of a Gantt Chart. Applications

In Project and Program Management, the Gantt Chart technique can be used to:

  • Display an overview of project activities.
  • Plan project activities.
  • Work out the critical path.
  • Give you a basis to schedule when the tasks should be carried out.
  • Allocate resources.
  • Communicate project activities.
  • Coordinate and manage project activities.
  • Monitor the progress of project activities.

Steps in creating a Gantt Chart. Process

  1. Determine and list the required activities / tasks. For example using the Brainstorming or Mind Mapping method.
  2. Create a rough draft of the Gantt Chart. There may be insufficient resources to perform all activities at the same time. On top of this, certain activities may require that other activities are finished first.
  3. Determine the dependencies and schedule the activities. Compare: Cause and Effect Diagram.

    • This ensures that when the planning has to be changed, the activities will continue to be performed in the correct order.

    • Ensure that dependent activities do not start until the activities they depend on have been completed.

    • Try to avoid increasing the critical path: the sequence of critical tasks from beginning to end that takes the longest time to complete. It is also the shortest possible time that the project can be finished in. Note that the critical path may change from time to time as activities are completed ahead of or behind schedule. Compare: Theory of Constraints.

    • Do not over-commit resources and allow some slack time in the schedule for unforeseen events. But critical tasks can have no slack, because they are part of the critical path.

  4. Calculate the number of man-hours for each activity.

  5. Determine who will perform the activities and adjust the number of hours when needed. Compare: RACI.

  6. Calculate the throughput time. Planning software will be able to do this automatically.

Gantt Chart versus PERTStrengths of the Gantt Chart. Benefits

  • Good graphical overview. Common technique. Easy to understand.
  • Small to medium size projects with no more than about 30 activities.
  • Can be supported by special project planning software to facilitate complex calculations and complex dependencies and conduct what-if analyses.

Gantt Chart versus PERT

Unlike the Gantt Chart, the Program Evaluation and Review Technique (PERT) has no calendar, so you can not see precisely when the activities should be performed. On the other hand, the dependencies between the activities in PERT are easier to follow. This is why for larger projects, usually PERT is preferable. Actually PERT uses multiple time estimates for each activity to allow for variation in activity times. The activity times are assumed to be random, with assumed probability distribution ("probabilistic"). They are represented by arrowed lines between nodes or circles.


Limitations of the Gantt Chart. Disadvantages

  • Projects are often considerably more complex than can be communicated effectively with a Gantt chart.
  • Gantt charts only represent part of the triple constraints (time, cost and scope) of projects, because they focus primarily on schedule management (time). Compare: Cost-Benefit Analysis.
  • Gantt charts do not represent the size of a project or the relative size of work elements, therefore the magnitude of a behind-schedule condition is easily misunderstood.
  • Software. Although project management software can show schedule dependencies as lines between activities, displaying a large number of dependencies may result in a cluttered or unreadable chart. Avoid using (heavy) grids in Gantt software as they distract the attention.

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