Difference Between PERT and CPM (With Table)

PERT vs CPM

The key difference between PERT and CPM lies in the fact that PERT stands for Program Evaluation and Review Technique, and CPM stands for Critical Path Method. PERT manages unpredictable activities, whereas CPM manages predictable activities.

In PERT, the prime focus is to plan and manage time, whereas, in CPM, the prime focus is to control cost and time. PERT is related to the events, but CPM is related to the activities.

Excellent project management skills play a pivotal role in the success of a business enterprise. These skills are crucial in the determination of the budget and time required for the achievement of a project’s goals.

PERT and CPM are the two standard statistical techniques adopted to ensure time consciousness and cost-effectiveness in the completion of projects.

However, the two techniques are different even though both lead to the designing of the project’s network.

 

What is PERT?

Project Management and Review Technique (PERT) is a statistical technique that is adopted for the determination of time that a project should take to complete.

Notably, the PERT technique is resourceful when dealing with unpredictable activities in a project since it accounts for uncertainties that might occur.

This is achieved by controlling the uncertainties in a manner that the time allocated for the project is not affected.

pert chart
PERT chart example
 

What is CPM?

Critical Path Method (CPM) refers to a management technique employed in the planning, coordinating, scheduling, and controlling a project’s activity in a quest to manage both time and cost of a project.

CPM technique is highly recommended for projects whose activities are predictable, for example, construction of a house.

The technique assesses the earliest and latest possible time to start each of the project’s activity.

CPM
CPM chart example

 

Comparison Table Between PERT and CPM Technique (in Tabular Form)

Parameter of Comparison PERT Technique CPM Technique
OrientationEvent-oriented technique.Activity-oriented technique.
Type of ModelProbabilistic model characterized by uncertainty in the duration of project completion.Deterministic model characterized by certainty in the duration of project completion.
The Technique’s FocusFocus on the time of completion of a project.Focus on the time-cost trade-off in a project.
The Crashing ConceptThe crashing concept is not applicable.The crashing concept is applicable.
AppropriatenessSuitable for high precision time estimation of projects that are unpredictable and whose activities are non-repetitive.Suitable for projects that are predictable and whose activities are repetitive. Time estimation for such projects is made under reasonable forms.

Main Differences Between PERT and CPM

Despite PERT and CPM techniques being used in designing a project’s activities network, the two methods remain very different.

The following are critical differences between PERT and CPM techniques.

Orientation

While the PERT technique is event-oriented, the CPM is an activity-oriented technique towards the determination of the cost and time to be taken from the start till the end of a project.

That is, the PERT network chart is constructed based on the events of the project at hand. On the other hand, a CPM chart network is developed based on jobs that make up the whole project.

Type of Model

The PERT technique is a probabilistic model characterized by uncertainty in the project duration. The tools in the PERT technique give several estimates for the calculation of the time of project completion.

The expected time for the end of the project is calculated from the optimistic time, most likely time, and the pessimistic time.

On the other hand, the CPM technique is a deterministic model. The technique’s deterministic tools offer an estimate that relates to the cost and amount of money available for a project’s completion.

Unlike the PERT technique, which provides three estimates, the CPM offers only one estimate.

The Technique’s Focus

The PERT technique lays focus on the time the project will reach its completion. Three estimates determine the time of completion of a project.

These include the optimistic or most promising time (to), the pessimistic or unfavorable time (tp), and the most likely or promising time ™.

Unlike the PERT technique, the CPM technique lays focus on the trade-off between the time and cost for the completion of a project.

To the project managers adopting the CPM technique, optimization of the cost of the project alongside the time of completion is essential.

Through this, project planners can adequately make decisions on which aspects of a project are trade-offs necessary.

The Crashing Concept

The crashing concept refers to the compression theory of shortening a project’s time of completion alongside the least additional cost.

Notably, the crashing concept does not apply to the PERT technique since there lacks certainty in time, making it hard to alter the activity duration.

On the other side, the crashing concept applies to the CPM technique.

With the certainty of the completion time, project planners and managers can alter the duration of a project alongside the least additional time.

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Appropriateness

The PERT technique is most suitable for research and development projects. These include projects where resources are always available as required.

A project with unpredictable activities is well managed using the PERT technique.

Additionally, the PERT technique is best used for the estimation of high precision time of duration of the project whose activities are non-repetitive.

On the other hand, the CPM technique is best suited for non-research based projects such as civil construction.

All projects whose activities are predictable and repetitive are well managed with the help of the CPM technique.

Additionally, the CPM technique is appropriated for the projects whose time estimations are under reasonable and flexible forms.


 

Frequently Asked Questions (FAQ) About PERT and CPM

  1. What are all the applications of PERT and CPM?

    There are a large number of applications of PERT and CPM. It is not possible to list them all at once but they can be classified into types.

    All types of applications of PERT and CPM are:

    1) Projects related to research and development (R&D)
    2) Maintain equipment
    3) Hauling of equipment
    4) Scheduling of construction projects like dam building, office building, etc
    5) Industry setup
    6) Machines, plants and systems designing
    7) Controlling large shops’ production
    8) Marketing new products and designing
    9) Manufacturing location shifting
    10) Organizing conferences, big programs, etc

  2. What are the similarities between PERT and CPM?

    PERT and CPM, both have a very similar approach. Their applications are similar.

    There are just two distinctions between them.

    1) There is only a one-time estimation in CPM for each activity. In PERT there may be three-time estimations for a single activity.
    2) CPM allows estimation of time and cost, hence controlling time and cost. PERT is a planning tool and only allows one to control time only.

  3. What are the applications of PERT and CPM?

    Applications of PERT and CPM and quite similar in approach.

    There are a lot of applications of PERT and CPM mainly:

    1) Construction projects like bridge, highway, dam
    2) Design a new product and market it
    3) Controlling production in large shops
    4) R&D projects
    5) Maintain equipment and hauling

  4. What are the advantages and disadvantages of PERT and CPM?

    There are many advantages and few disadvantages of PERT and CPM.
    Advantages:
    1) Helps you map all details in a diagram (easy to organize and measure the number of tasks and timelines)
    2) A critical path would help you determine how an activity would affect the project deadline
    3) A PERT diagram helps you think logically about resources and deadlines.
    4) Helps you understand and measure the details that are required to be accomplished to not miss the deadline
    5) Help you understand which paths can be delayed and which paths need more focus to not miss the deadline
    6) Minimize the time and cost of the entire project.
    7) Optimal utilization of resources

    Disadvantages:

    1) Works best when a person has the experience and understanding of the project otherwise the diagram is less useful.
    2) It only works best when the team has the experience to estimate the accurate timeframe.
    3) Diagram becomes complicated if the project is too big.
    4) If the project is far too bulky and lengthy, all the map outlines become incomprehensible.
    5) It cannot properly monitor the allocation of resources.
    6) Inability to control the schedule of the person involved in the project.
    7) Very difficult to redraw entire CPM if there are sudden changes in the implementation of the plan



 

Conclusion

The PERT technique is an event-based time estimation technique for projects whose activities are unpredictable and non-repetitive.

On the other hand, the CPM technique is an activity-based time and cost estimation technique for projects whose activities are predictable and repetitive.

Given the differences between the PERT and CPM techniques of project management, one can easily tell the optimal technique for whatever project is as at hand.


 

Word Cloud for Difference Between PERT and CPM

The following is a collection of the most used terms in this article on PERT and CPM. This should help in recalling related terms as used in this article at a later stage for you.

pert and cpm
Word Cloud for PERT and CPM

 

References

  1. https://ascelibrary.org/doi/abs/10.1061/(ASCE)0733-9364(2000)126:3(219)
  2. https://books.google.co.in/books?hl=en&lr=&id=ODApoTanj4IC&oi=fnd&pg=PA1&dq=PERT+and+CPM&ots=y5xKkVNA5a&sig=ey7-Vc_m_riudGbO5nwm96vWDxw&redir_esc=y#v=onepage&q=PERT%20and%20CPM&f=false