PERT vs. CPM - Comparison and Differences

The project may be of different sizes, such as small, large, complex, etc. The aim of any project manager is to create a management plan to complete the project within a given time frame. CPM and PERT are the analytical tools used in project management for the efficient management of project activities.

In terms of project management, CPM stands for Critical Path Method, and
Pert stands for Program Evaluation Review Technique.

The Critical Path Method is a project management algorithm used to schedule the project tasks, while the Program Evaluation Review Technique is a project management tool that is used to calculate the time consumed to successfully complete the project activities.

Critical Path Method (CPM)

The critical path method falls under the time management of project management. CPM is a project management tool used to design and generate a project schedule. This method produces approximately precise start and finishes dates of a project by running multiple analytical techniques like the critical path method, critical chain method, and resource optimization.

CPM is used to estimate the minimum project duration and minimum resource consumption. This helps with determining the flexibility of project activities and paths. Resource limitations are not considered in this case.

Flexibility in a schedule is measured by the time a scheduled activity may be delayed or drawn out from the start date. This process is termed "Total Float." While using this method, depending on the constraints applied, the critical path can have a negative, zero, or positive total float.

PERT vs. CPM - Understanding the differences

In project management, PERT and CPM share a lot of similarities, but the following differences differentiate PERT from CPM.

Program Evaluation Review Technique (PERT)

Program Evaluation Review Technique (PERT) is a project estimating and scheduling technique. It is a probabilistic technique used to indicate the expected time for the completion of the project.

This technique can’t be used to estimate the earliest time for completing the project since it considers all the uncertainties of the project and takes all the risks involved into account. It is a probabilistic network analysis method used to plan and schedule uncertain project activities.

PERT vs. CPM - Applications

Since PERT and CPM share most of their similarities, they are applicable in various fields of network analysis. Commonly shared applications of PERT and CPM are as follows:

- Marketing programs.

-  Marketing new products.

- Setting up of new industries.

- Scheduling of future projects.

- Large-scale production control. 

- Resources maintenance of a project.

- Planning of production of new products.

- Advertising campaigns and management.

- Construction, research, and development projects.

- Maintenance of resources like financing and staff.

PERT vs. CPM - Advantages

CPM was developed in 1957, and PERT was delivered in 1958. They have been in use for a long time due to the lack of disadvantages and the wide availability of benefits. 

Advantages:

- Optimize resource consumption.

- Helps in improving product productivity.

- A CPM predicts how activity affects the project.

- Helps you design a clear map with all details of the project.

- Can be used to optimize the time and cost of the project to a minimum.

- You can easily measure and organize the project tasks with a timeline.

- A PERT chart helps you logically process, assign, and manage the resources.

PERT vs. CPM - Disadvantages:

- Requires good knowledge for understanding the generated chart.

- PERT is time concentrated but does not consider the cost.

- In CPM, estimation of the project timeline is difficult to process.

- For small projects, PERT charts can’t be scaled easily.

- For massive projects, charts become complicated.

- Allocation of resources is not precise.

How to find the critical path

In order to find the critical path of a project task, the duration of critical and non-critical tasks must be considered. The following is a breakdown of steps that help you define the critical path of a project.

1) List all project activities.

Let’s first list down all the project tasks and activities that are responsible for producing deliverables by creating a breakdown work structure. This list lays the foundation for the rest of the critical path.

2) Underline project aims and tasks.

Depending on the tasks listed, determine the tasks that are dependent on one another. This helps you know what tasks can be executed with other tasks to more efficiently organize tasks and activities.

3) Design an organized chart for project tasks.

Taking the list designed and highlighting the dependent tasks, now design an organized system chart depicting the record of activities. Draw boxes for each task and use arrows to show the dependency of tasks. You can include other components like time until the general schedule of the project is figured out.

4) Evaluate the time taken to complete each task.

Estimation of task duration can be done by

- Estimation based on experience.

- Estimation based on previous project data.

- Estimation based on industry standards.

Alternatively, the estimation can also be done by predicting the earliest date of start and finish together with the late start and finish timings. To calculate early start and finish dates, you use Forward Pass, and for late start and finish times, you use Backward Pass.

5) Identify the critical path of the task.

Once you are done with listing, designing, and evaluating the tasks, you now have to identify the tasks that form critical paths. Considering the end time of each activity in the sequence, determine the duration of the entire sequence. The sequence of activities with the maximum duration is the critical path of this scheduled activity.

Since the critical paths are taken care of, it becomes easy to design a project schedule. The above tasks performed serve as the key tasks in building a proper schedule.

6)  Measure the total float.

Float, also called stack, is the flexibility given to a task. It shows to what extent a project can be delayed without affecting the sequence of project tasks and activities.

Measuring the float can determine how much flexibility a project can have. Float can help you cover unexpected project issues and project risks.

Critical tasks that have zero floats are the ones that have fixed dates. Project tasks and activities with positive float are in the category of the non-critical path. They can be delayed without affecting the actual project timeline and milestones. By skipping these tasks, you can save time only when you have a shortage of time for the project.

You can follow manual methods or use the algorithm to calculate the float.

The Total Float (TF) of a project is the difference from the Latest Finish (LF) date to the Earliest Finish (EF) date or, the Latest Start (LS) date to the Earliest Start (ES) date.

[TF = LF - EF] or [TF = LS - ES]

PERT vs. CPM - Conclusion

With a complete understanding of this article, now you are clear about the working differences, advantages, and disadvantages between CPM and PERT.

The PERT method is more precisely used for projects with unpredictable and non-repetitive activities. On the other hand, for projects with predictable and repetitive tasks, CPM is precisely applied.

PERT is an activity-oriented technique that is also cost-oriented. CPM is an event-oriented technique that focuses on cost control.

By understanding their differences and applications, you can now be more aware of which technique is to be used under what circumstances.

These techniques are most helpful in producing a project plan and also in scheduling the project tasks.

These techniques can be applied and implemented, making use of the wide availability of online tools that help users automate and design their tasks.

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