PERT And CPM: An Easy Overview And Differences (2021)


If you are in the civil engineering or construction field, you are highly probable that you are familiar with PERT AND CPM. Even for project planning and control, you are supposed to know about PERT and CPM. Nowadays, they are used widely for project planning and control in large developmental projects. And so, this article gives u precise knowledge of PERT and CPM. 

  1. Comparison chart
  2. Definition
  3. Pert analysis  
  4. Key differences
  5. Advantages and disadvantages

1. Comparison chart

                        PERT                     CPM  

What is it?      Planning                 Control 

                       Technique               Method  

Evolution        Research                Construction  

                        Development              Project      

Focus              Time                        Time and cost  

2. Definition

PERT refers to Program (Project) Evaluation and Review Technique. It is generally a visual project management tool that is used in project planning.  It involves planning, organizing, integrating and authorizing uncertain activities. It provides detailed information regarding the project’s tasks, the minimum time required for completing individual tasks, and the average time required to complete the whole project. The variable used in PERT technique is time. The PERT Analysis shows you the critical path of a project.

The critical path is a set of activities that will cause an end date delay of the project if any one of them is not finished on time. There may be more than one critical path, and the critical path can vary depending on the project. Pert method includes uncertainty by making it possible to schedule a project while not knowing precisely all the details and duration of all the activities. It is mostly used in projects where time is the major important factor than cost. PERT was first developed by the United States Navy in 1958. 

3. Pert analysis  

PERT uses a three-point estimation. They are optimistic, Most likely, and pessimistic.  

Pert method = (1×P 4×M 1×O) /6  

Here, we give more importance to most likely. 


PERT method = (1×P 4×M 2×O) /7  

                      = (1×P 6×M 1×O) /8 

We can also find out the standard deviation in PERT in order to calculate average variation.  

 Standard deviation = (O – P) /6 

In order to draw PERT chart, three steps should be followed.  The first step is to draw the activities. In the second step, you need to number nodes and prioritize.  In the last step, you have to add your chart’s duration to find out the critical path on that pert network. 

CPM full form is the Critical Path Method. In CPM, we are supposed to assume that project duration is certain.  It is generally used to ascertain the earliest possible starting time of every activity.  The queue is avoided by differentiating critical and non-critical activities.  This also helps in reducing time. Any activity can be treated as a critical activity if any delay of such can result in a delay of the whole process. CPM is a project technique developed in the late 1950s by MORGAN R. It is mostly found in construction, research projects, engineering, aerospace, plant maintenance, and software development.

A CPM method developed should contain four values. There is a list of activities required to finish the project, the duration of each activity to complete, and any dependencies between the activities and milestones to be achieved. Using this, the longest path from the activities to the milestone or endpoints is found. This process also decides activities that are critical. It determines the least time to complete the project. 

4. Key differences

Some of the major differences between PERT and CPM are given below:  

1.    PERT is a visual project management technique where we plan, schedule, organize, coordinate and control uncertain activities. Whereas CPM is a statistical technique where we plan, schedule, organize, coordinate and control well-defined activities.  

2.    CPM is a method used to control cost and time. Unlike PERT, which is a technique used for planning and controlling time. 

3.    PERT can be said as a development and research project tool, while CPM is a construction project tool. 

4.    PERT is aligned towards events while CPM is set according to activities.  

5.    A settled model will be used in CPM.  A probabilistic model is used in PERT method. 

6.    PERT uses three-point estimation such as optimistic, most likely, and pessimistic.  Whereas on the other side, there exists only one estimate in CPM.  

7.    PERT is used where time is highly valued than cost whereas, for reasonable time estimate projects, CPM method is apt. 

8.    PERT is used in case of unpredictable activities. On the other hand, CPM is used in the case of predictable activities.  

9.    PERT is used for jobs that are non-repetitive in nature. In distinction, CPM is used for jobs that are repetitive in nature. 

10.    There is no differentiation between critical and non-critical activities in PERT. Differentiation exists in CPM.  

11.    CPM is suitable for non-research projects, while PERT is apt for research projects.  

12.    Crashing technique is used in CPM while it is not used in PERT. 

5. Advantages and disadvantages

A PERT chart helps you to create endpoints or milestones of the project. You can also identify any possible obstacles and quickly address them. This is the main PERT advantage. The disadvantage of PERT includes the absence of time focus. 

A CPM chart gives a precise graphical form of projects. It saves time and helps to compare our current position with the planned position. Coming to the disadvantage of CPM, it will be really hard to estimate the completion time and critical path for huge projects.  


The difference between PERT and CPM is reduced to a lesser degree. Nowadays, PERT and CPM are used in a complimentary way. 

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