What is PERT in Project Management ?

by StarAgile

October 13, 2020
Category Project Management

PERT in Project Management, a Detailed Study

PERT is the tool which will help you to sort out the activities by calculating the real schedule and to find out many events and milestones of every activity that we do. 

Ever thought of how to solve the problems in real life? Ever wondered when you go shopping on how to complete all the activities in the best possible way. Then you are reading the right blog, in this blog, we will discuss how to manage complex things easily and simply. It does not only apply to daily life scenarios but also to work-life where you can use this tool to solve problems and complex scenarios by using this tool. 

Yes, we are talking about the tool which will help you to sort out the activities by calculating the real schedule and to find out many events and milestones of every activity that we do. 

Yes we are talking about the PERT tool. After reading this blog you will understand how to use the PERT tool to solve many problems. To know more about the PERT tool you can register for the PMP certification online.

It is one of the tools used to manage the project management dependencies

What is PERT, Common Notations and Basic concepts 

The project is a series of complex activities that are interdependent to make it successful. These series and parallel tasks form the network diagram. 

Project tracking is important in managing projects and PERT is used in evaluation and review. 

PERT Diagram 

PERT, a network diagram in which the activities and milestones are embodied on the line nodes respectively. 

The sample PERT is shown as a diagram below.

PERT chart Diagram

The difference between the critical path method (CPM) and PERT is the former one uses the fixed time estimates for the activities and does not consider the variations in the time. It only helps us to determine the longest path or the critical path in the network diagram. However, the latter one uses the randomness in the time completion. 

In PERT the nodes are numbered by 10 as any other activity can be inserted between the nodes without changing the network diagram itself. The activities are labeled as alphabets with the expected time to complete the activity. To know more learn about PMP online training.

The steps required to perform the PERT are as follows,

  • Activity and milestones identification - The activities are the tasks required to complete the project. Milestones are the events that specify the activity begin and completion. The activities are put in the table and then expanded to allow for the time and sequence.
  • Evaluating the sequence of the activities - The simple tasks can be sequenced quickly but other tasks are complex may require breaking down to smaller tasks and then sequence them
  • Constructing the PERT diagram It is made by using the arrow line as a sequence of activities and the milestones as nodes or the bubbles in the diagram. It requires more than 2 iterations to do these activities but some software will do it quickly from the table that you make.
  • Activity time Estimating - It recognizes the randomness or the uncertainty in estimating the time for each activities. There are 3 possible time estimates in PERT they are as follow,

1.Optimistic Time (OT) - This time is the shortest possible time to complete the projects. It is the 3 standard deviations from the mean that is it has approximately 1% chance that the project gets completed at this time.

2. Most Likely Time (MLT) - This is the time which has the highest possibility of the completion

3. Pessimistic Time (PT) - It is the longest possible time for activity completion. Again the 3 Standards deviations from the mean are used to calculate the pessimistic time.

The PERT assumes the beta probability distribution to complete the time estimates. These are calculated as Expected time and the formula is,

Expected Time (ET) = (OT + 4 * MLT + PT) / 6

The ET is shown in a network diagram.

Variance = 6 SD (standard deviations) between the OT and PT as shown below

[(PT - OT / 6]2

Critical path determination – It is the longest possible time to complete the project. We need to find the four quantities in determining the critical path they are the Earliest Start Time, Earliest Finish Time, Latest Start Time, and Latest Finish Time. They are calculated by using the Expected time of each activity. The Earliest Start and Finish time are calculated by working forward on the network diagram. The Latest Start and Finish time are calculated by working backward on the network diagram.

Updating the diagram - As the execution starts, the PERT diagram is updated by the actual time to see what the deviation is. In case there are delays then additional resources are put to manage the time.

You can learn more about this tool by doing a PMP certification course. 

PERT Floats

The total float (TF) is the thing to determine how long the activity can be delayed without modifying the project completion date. On the critical path, the total float is zero. Total float and slack can be used interchangeably. 

There are 2 methods to calculate the total float.

TF = Late – Early (both are start dates)


TF = Late - Early (both are finish date)

Free float (FF) is determined as to how long the activity can be delayed without delaying the early start date of the successor activity.

FF = ES of next activity - EF of the current activity.

The project manager is responsible for doing the PERT analysis and if you want to do it yourself look for the project manager certificate online.

How to schedule with a pert chart based on pert project management scenarios

The PERT chart helps a great deal in resolving the complex project into smaller activities with expected timelines. Once you have the PERT that works for you, the activities and timelines will ensure that you are cutting down on the timelines and meet the target within the project completion date. Once you are meeting the timelines then you are cutting down on the cost on the operations and ensure you are not penalized for the late delivery of the projects.

Take up the scenario of software development for making an application where you need to break down the development, test, and production activities into smaller features based addition activities. You can use the PERT network diagram to sequence and write the timelines for each software development life cycle activities as shown in the diagram below.

Program Evaluation Review Technique

PERT Chart Example 

When and how to draw pert chart example with critical path explained

When to draw a PERT network chart with a website construction example is as shown below,

  • Plan for identifying the activities and timelines
  • Plan for the milestones and sequence the activities
  • Identify the critical path that is the minimum time to complete the project
  • Identify the parallel tasks and other non-critical tasks
  • Identify all the paths on the PERT network diagram
  • Identify the slack time and the floats
  • To evaluate the expected time of completion of the project.

Advantages of PERT Chart

• Activities are mapped to find out the timelines of the project completion

• The most likely, most optimum and pessimistic times can be calculated

• You can evaluate the resources required for each activity

• Also provides the critical path of the activities.

• Helps in setting goals for the project

• Helps to understand the slack period of non critical activities.

• Helps to understand the activities independently and in combination

• Helps in doing the what-if and other critical analysis of the project

Disadvantages of PERT Chart

• It is time intensive and resource intensive to develop the PERT chart

• It is sometimes subjective especially when it comes to the date of completion of the activities and allocation of the resources.

Before we wrap, 

Understood what is pert in project management, now know the difference between PERT and CPM. 

PERT is used extensively in the manufacturing industry with great success and from the past 2 decades, the PERT is used in the IT, Embedded systems, Hi-Tech, and software industry. It has helped many companies in managing projects to produce products or services in a timely fashion. 

CPM is part of PERT and PERT is a broader topic that helps the project manager in managing the schedule by calculating the critical path, the floats, and slack period and estimating the expected time from the optimistic, pessimistic, and most likely time. 

The CPM is just used to find the longest path it takes to complete the project which is the critical path. PERT is based on the events based, uses a probabilistic model, unpredictable activities and three-time estimates whereas CPM is activity-based, uses a deterministic model, for predictable activities, and uses one time estimates.

Are you curious to learn PERT in a real-time scenario then why wait? Do register for training with StarAgile for the PMP certification training course.