Critical Path Method (CPM) – The Ultimate Guide To Critical Path Method

Critical path method (CPM) is the most important concept to understand for the PMP Exam. Once the project manager defines the project activities, activity duration and figure out the sequence of activities in the project, it is time for the project manager to see and analyze the critical path in the project.

This is done by creating a network diagram using all the activities, activity duration and dependency between the activities. And finally figuring out the longest path in the project, which is called critical path in project management terms.

Critical Path Method (CPM) and Critical Path

Critical path method (CPM) is the method, which project manager uses to figure out the critical path in the project.

The Critical path is defined as the longest path in the project. or

Critical path can also be defined as the shortest duration in which the project can complete.

What does it mean?

Critical path means that, the project manager do not have any luxury of delaying the project, when performing the activities on critical path. So every activity on the critical path must complete on time for the project to complete on time. A delay in any of the activities on critical path, will delay the whole project.

So critical path can also define as the collection (path) of activities that will delay the whole project, if any of them are delayed.

Well. But why should I know about it as a project manager?

Importance Of Critical Path For The Project Manager

As project manager your main objective is to look at the activities in the project, for any slippages and to correct them as needed. Especially with respect to critical path the project manager has to understand two points.

  1. Understand the critical path and make sure each activity on the critical path is completed on time. Knowing the critical path of the project will help the project manager to use any of schedule compression techniques to keep the critical path activities on track in terms of timelines.
  2. Understand the activities which are not on the critical path. This will give a room for the project manager to play with the activities, if there are any delays with any of them. Meaning that this gives project manager some amount of freedom to consider the delays in one or more activities without impact the overall timelines of the project.

I got it know. But still would it be so important for me to understand to a great detail about it.

Yes. You need to understand the critical path method (CPM) completely in order to implement this in your project while performing the schedule management. Also from PMP exam perspective this concept is at most important. So to understand this in more detail we will traverse through a simple example.

Steps To Find Out Critical Path Using Critical Path Method (CPM)

Here are the simple steps to find out the critical path in the project.

Step 1 – create a network diagram

With the help of activities, activity durations, dependencies create the network diagram using either of the methods activity on arrow (AOA) or activity on node (AON).

To keep it simple, we have followed precedence diagraming method (PDM) or activity on node (AON) method to create the network diagram in this blog post.

Step 2 – Figure out all the paths in the project network diagram

List down each of the paths in the project. Each path in the project represents activities to be performed in parallel with other paths.

Remember here that lot of PMP aspirants get confused that the paths are alternative to one another to finish the project. But this is not true.

All project activities are scatter across these paths based on the dependencies between the activities. And hence every path and every activity in each path must complete for a successful closure of the project.

Step 3 – Calculate the length of each path.

As we have charted out different paths exists in the project. It is time to calculate the duration of activities in each path, which we call it as the total length of the activities in that particular path.

Step 4 – Find out the critical path, which is the longest path in the project.

Eventually the longest path is called as critical path in the project. Meaning that any delay in the activities that are existing on critical path will delay the whole project.

Now since we have seen the steps to calculate critical path using critical path method (CPM), let us look at a simple example to understand it practically.

Critical Path Method (CPM) Example

Critical Path Method

Let us take a simple example of baking a pizza at home to introduce some fun while learning this concept.

Activity ID Activities Duration
(in Minutes)
Predecessor Notes
A List down the ingredients required 5 Start All required ingredients for baking the pizza
B Purchase the spices, mozzarella cheese and veggies 30 A purchase from nearby store
C Mix the dough and keep it ready 20 A A is predecessor as you need ingredients such as yeast to mix with dough
D Bake the pizza 30 B,C Bake the pizza in the oven
E Decorate (present) and Serve it 15  D Present it to make the looks wonderful

Step 1 – create a network diagram

Let us create the network diagram with the above activity information.

Step 2 – Figure out all the paths in the project network diagram

Now from the above diagram let us figure out the paths as follows.

Path 1:  START=>A=>B=>D=>E=>Finish

Path 2:  START=>A=>C=>D=>E=>Finish

Step 3 – Calculate the length of each path.

Now calculate the length of each path by adding the activity durations in that path.

Path 1 Length = 5+30+30+15 =80 mins

Path 2 Length = 5+20+30+15 = 70 mins

Step 4 – Find out the critical path, which is the longest path in the project.

It means that the total duration of activities in path 1 is 80 mins.

And the total duration of activities in path 2 is 70 mins.

So as we learned the critical path is the longest path (duration) in the project. In other words critical path is the shortest duration within which the project can complete.

So path 1 is longest duration path in the project. Hence the activities in path1 are considered to be on critical path and requires to be complete on time in order for the project to complete on time.

Conclusion

So Critical path method (CPM) is an important concept to understand both for the PMP exam and also for the project management in your projects.

Also we have seen what a critical path method is and also learn that project manager has to focus more on activities that are on critical path to avoid any delays in the project.

Finally we have seen the steps to calculate the critical path in the project and we calculate the critical path with the help of an example.

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