The Gantt Chart

Developed by Anders Thorp Sørensen

This article will introduce the Gantt Chart by giving a basic introduction to the understanding of the Gantt Chart, explain the use of a Gantt Chart in practice as well as pointing out some of the limitations. The Gantt Chart was the first time created by a Polish engineer named Karol Adamiecki (born March 18th 1866). Approximately 15 years later, it was also created independently by an American engineer called Henry Gantt (born in 1861) . It is a tool that is very commonly used in project management as it is great for displaying different activities against time. Depending on how much information that is put into the Gantt Chart the Gantt Chart can become increasingly complex to use. Because of todays technology it has become much easier to create a Gantt Chart and get an overview of the interdependencies of the different activities within a project as many different computer programs can help to create a Gantt Chart fast and easy.

It can however be confusing to create a Gantt Chart through the use of different computer programs as there are a lot of different informations that can be put into a Gantt Chart. So choosing the right program compared to how detailed the Gantt Chart should be can be a hard choice. As many programs are available it can be hard to find a program that fits the specific needs one might have. Therefore a list of usable programs can be found in the end of this article.

History of the Gantt Chart

The first version of the Gantt Chart was created in the mid 1890's by the Polish engineer named Karol Adamiecki who was born on March 18th 1866. The world known version that we know today was developed approximately 15 years later than the first version, by an American engineer and consultant called Henry Gantt who was born in 1861. This version of the Gantt Chart was created by Henry Gantt while he was working with the construction of Navy ships during World War One and is today known as "the Gantt Chart". Already from the mid 1920's the Gantt Charts were acknowledged as a production planning tool. In the beginning the Gantt Charts were created by hand which caused a lot of re-work when a change in the current planning happened. Though the Gantt Chart were a popular tool from the beginning, it encountered some problems with the limited handling of information and it was speculated that computers would replace the Gantt Charts. Then in the 1950's and 1960's the Gantt Chart lost its popularity as the large scale production complexity were considered too complex. Today we have the technological advantage of computers and a lot of different project managing software to help create a Gantt Chart which can be updated a lot easier than back in the days where it had to be done with a pen.

Though the use of technology seems very tempting as it eases the manual work a lot, a project director of a large construction company commented that: "I believe that computer-based project management has set the subject back 20 years". Even though this quote is 14 years old, it reminds us that exaggerating something whether if it is new technology or something else, can turn out to be disadvantageous.

Basic understanding

The Gantt Chart is a type of bar chart where the bars are represented in relation to a x-axis and a y-axis. The x-axis represents the time which can be hours, days, weeks, months etc. depending on the timespan of the project. The y-axis represents the number of different activities or tasks that has to be performed in the project. The bars in the chart each represents an activity and the length of the bar is dependent on the amount of time estimated for that specific activity. The different activities can be dependent on one another. There are several types of dependencies and Allan Orr identifies three of them as:

• Finish to Start - This means that one activity must be finished before another one can start.
• Start to Start - This means that the activities has to start at the same time but not necessarily finish at the same time.
• Finish to Finish - This means that the activities has to finish at the same time but not necessarily start at the same time.

There are however more types of dependencies. One that is missing from the dependencies that Allan Orr has identified is:

• Start to Finish - This means that one activity has to start before another one can finish

In addition to the above mentioned dependencies there is a term known as slack or float. Float is the buffer between when an activity can be completed and when it has to be completed. An activity that is on the critical path (see The Critical Path Method (CPM)) has no float. In addition to float there a sub-term called free float which is the amount of time an activity's start date can be postponed before it will delay its successor activity's start date. More on what a successor activity is in the section "The Gantt Chart in practice".

An example to show dependencies could be a project where you need to turn on the light. It is not possible to turn on the light before a lamp has been purchased and installed so using the switch will have to wait until the lamp has been installed. If you need to buy a light bulb this can be done in advance if you know what type you need. Otherwise, buying the light bulb would have to wait until the lamp has been purchased but it would be possible to buy the light bulb before the lamp has been installed. This means that buying the light bulb and installing the lamp can begin at the same time to save time (Start to Start).

There is also the case where an activity can begin after a certain percentage of its predecessor activity has been completed. A situation could also arise where an activity has been completed but it is pending an approval or similar which results in the next activity not being able to start. This is called dependency with lag time.

The purpose of the Gantt Chart is to present a chart that simple and quickly provides the viewer with the information needed to analyze the project and give an overview of the time span of the project, the time span of the different activities within the project and show the interdependencies of the activities.

One thing to remember about the Gantt Chart however is that alone the Gantt Chart is a blunt instrument. It is used as a presentation of plans but the Gantt Chart itself does not cover why of the planning.

The Gantt Chart in practice

Figure 1: Example of a basic Gantt Chart, Source: http://www.ganttchart.com/BasicGanttExample.html

Figure 2: Example of a Gantt Chart created in Visio, Source: http://gioielleriaricci.it/gif/photos/index.php?p=26

In order to use a Gantt Chart one must have a detailed plan for the project. It is crucial that the duration of each activity within in the project has been estimated and that the interdependencies has been identified. Furthermore it is needed to know what resources are able to perform the activities as the same resource is not able to perform several activities at once. When the data is put into the Gantt Chart it should be easy to see the start and finish of all activities within the project and also see the start and finish of the project itself. It should also be possible to get an idea of which activities are dependent on each other. In Figure 1 and 2 it is hard to see exactly which activities are dependent on one another. However, it is assumed that one activity starts as soon as possible when its predecessor has been completed and that the planning of each activity does not inflict with the different dependencies. One way to help get an overview of the activities can be through color coding.

Figure 1 illustrates the use of a simple Gantt Chart from a Security & Access Control project. As it can be seen in the figure, all activities are marked with a yellow triangle and a number to indicate the start date of the activity. Each activity is also marked with a green triangle and a number to indicate the planned end date of the activity. In the left column the name of each activity is written and in the right column the responsible sub contractor for each activity is listed.

Figure 2 is an example of how a Gantt Chart looks in Microsoft Visio which is a program that should be available for free for students at DTU. In this example it is very fast to see how long each activity takes and the planned start and end date for each activity.

Both Figure 1 and Figure 2 illustrates a simple way of using a Gantt Chart in practice to get an overview of the activities that has to be done. As mentioned more details can be put into a Gantt Chart i.e. the way activities are dependent on each other. In order to see the interdependencies of activities in the project, arrows between the activities can be added to visualize which activities are connected. A simple illustration of this can be seen in Figure 3.

Figure 3: Example of dependencies between activities, Source: http://www.gantt.com/creating-gantt-charts.htm

Figure 3 illustrates that an activity can have both a predecessor activity and a successor activity. A predecessor activity is an activity that needs to be completed before it is possible to start on the next activity (Finish to Start dependency). In the example with the light, buying the lamp is a predecessor to installing the lamp. A successor activity is an activity that cannot start until the current activity has been completed (Finish to Start dependency). In the example with the light, turning on the switch is the successor activity to both installing the lamp and buying the light bulb. Depending on the size of the project an activity might have several predecessor activities and several successor activities. By adding the linkage between the activities to the Gantt Chart it also becomes possible to identify the critical path in the project. The critical path is the longest sequence of tasks that has to be completed in time for the project to be finished on the due date, or said in another way, it is the sequence of tasks that determines the earliest possible completion date of the project (See The Critical Path Method (CPM) for more information on this topic).

When the Gantt Chart has been made and it is possible to have a overview of the project it is very important to keep it updated. When a change to the project happens it is very important that this change is somehow converted into information that can be put into the Gantt Chart and thereby update the Gantt Chart and see what effect the change has on the project. Some changes might not affect the timetable of the project but other changes might be crucial for the outcome of the project and change the timetable drastically. If these changes are not put into the Gantt Chart but the Gantt Chart still functions as an overview of the project it can have severe consequences.

Because the Gantt Chart visually presents a projects information in regards to what needs to be done at what time, it is practically applicable in almost any situation where an overview of the activities and their time span though it might become quite complex to use for big projects.

A short step-by-step guide on how to create a Gantt Chart

• List all the activities that needs to be completed
• Write down the earliest start date for each activity
• Write down the duration of each activity
• Write down if any activities are dependent on other activities to be completed
• Make a column where you list every activity
• Make a column for each day/week/month you think you project will take
• Plot in your activities with horizontal bars with the length of the duration of the activity
• If a task cannot be started before another one is completed, show this by starting the second task when the first is completed.

You can use color coding to "sort" the activities, and connect them with arrows to show the interdependencies.

Below video is a guide on how to create a Gantt Chart :

Limitations

As with any other tool the Gantt Chart also has its limitations. Some of these limitations has been identified here.

• The Gantt Chart requires the WBS (Work Breakdown Structure) to have been done (see Work Breakdown Structure (WBS) for more information on this topic). Before this it makes absolutely no sense to try and create a Gantt Chart because the information regarding which activities that should be put into the Gantt Chart will not be available.
• There is a risk the the Gantt Chart can become complex and be confusing to look at for big projects. If a computer is being used and the Gantt Chart takes up more space than a single screen it can be confusing to get the needed overview of all the activities.
• Costs is not taking into consideration when using the Gantt Chart. Costs is usually what most companies tend to focus on and it is therefore a weakness that the Gantt chart is completely ignorant when it comes to costs.
• The amount of work needed for each activity is not specified. It is just an estimation of the time span. Even though the amount of work needed has been calculated and estimated it is only the time estimation which is presented in the Gantt Chart.
• It does not see the weak links between the different stages in the project. The Gantt Chart can show the links between activities but it has no information in regards to how sensitive these links are.
• The Gantt Chart does not include information about the location of the work that has to be carried out. For information regarding a method that includes the location of the work see Location Based Scheduling (LBS).

The biggest limitation of the Gantt Chart though must be that alone the Gantt Chart is nothing more than a blunt tool.

Tools for creating a Gantt Chart

Free to use (for DTU students)

This section covers a list of software that can be used to create a Gantt Chart. There are many more "pay to use" programs than listed here and it is probably possible to find more "free to use" programs at well but the two listed here are the ones who I found to me most trustworthy.

• Microsoft Visio - One of the easier tools to use if you need a simple Gantt Chart, which should be available from Microsoft Dreamspark for students at DTU.
• GanttProject - Free to use program. There is an instructional video on the webpage.

Pay to use

• Microsoft Excel - If you have the Microsoft Office package you will also have excel.
• MindView - There is a free trial period of 30 days.
• Smartsheet - There is a free trial period of 30 days.
• Microsoft Project - Very expensive but also very professional tool.

Conclusion

If there is need for a tool that can provide an overview of the time span of a number of activities and how they are dependent on one another then the Gantt Chart will be a fine choice. If the project is a small project the Gantt Chart might be one of the best tools that can used. However, if the project is big with many different activities and interrelations between these activities the Gantt Chart might not be the best solution depending on the technology available as it tends to become too complex to get an easy overview. Before starting on the Gantt Chart it is important that the pre-work like making a project plan (see Program evaluation and review technique (PERT)), WBS (see Work Breakdown Structure (WBS))etc. has been done as the Gantt Chart will not be able to do this and if something is left out the Gantt Chart will not be able to show this. Remember, to make a Gantt Chart is not the first thing to do when starting a project.

Annotated Bibliography

• Orr, Alan (2003) "Uncharted Territory - This article gives a great overall explanations of the different aspects of the Gantt Chart. It also discusses something about risk mitigation which has not been mentioned in this wiki article.

• http://www.gantt.com/index.htm - If you need more information regarding what a Gantt chart is, how to create a Gantt Chart or what software to use both for creating Gantt charts but also for project management in general then this page is a good place to start.

• Maylor, Harvey (2001) "Beyond the Gantt Chart: Project Management Moving on - This article talks about project management in general and looks at other ways of managing projects than by the use of a Gantt Chart. The article seems very critical about the Gantt Chart and brings another perspective to the topic.

• Wilson, James M. (2003) "Gantt charts: A centenary appreciation" - This paper describe the history of the Gantt Chart from the beginning of the 19th century. It is a very interesting read if you want to know more about the development of the Gantt Chart from then to now. It also provides a view on how Gantt Charts is used now since it regained its use after the 1960's.