What Is PERT and CPM

Difference Between PERT and CPM: Full Form

Any project involves scheduling, controlling, and planning several interrelated activities using limited resources: money, workforce, material, and time. The project may be complex, large, and small, such as a shopping complex, nuclear power plant, highways, housing, etc. The main aim of project management is to complete the task within the time limit.

They are following two methods used for planning, scheduling, and controlling the activities


Both techniques are used for project management, but there is a significant difference between PERT and CPM.

Difference Between PERT And CPM

The following are the key difference between PERT and CPM techniques,

It is Event oriented technique  It is Activity oriented technique  
PERT manages unpredictable activitiesCPM manages the predictable activities  
It is focused on time control  It is focused on cost optimization
It is suitable for non-repetitive projects like building construction, road, infrastructure, maintenance work, etc.  It is suitable for repetitive projects like building construction, road, infrastructure, maintenance work, etc.  
It was developed in 1958.  It was developed in 1957.  
It is a three-time estimate  It is single time estimates  
It is a probability model.  It is a deterministic model  
It applies to the crashing concept.  It does not apply to the crashing concept.  
PERT and CPM Comparison

Read More: Cost Estimate | 10 Types of Cost Estimation

What Is CPM?

CPM complete form is the Critical path method.

The critical path method is a project managing tool. It is a one-type network diagram showing the different activities in a step-by-step algorithm, methodology, and technique for project planning. CPM was developed by DuPont company. Technically, the critical path shows the longest track of the network. It has the least amount of float.

In project management, a float is defined as the amount of time a task can be delayed without affecting subsequent and project completion tasks. The critical path method activities are shown in a network diagram as a network of precedence relationships using movement on the node network.

CPM follows the deterministic approach. It is calculated as a single estimation time for activity.

What Is PERT?

PERT full from is Program Evaluation and Review Technique.

A PERT chart is a project management tool that shows a graphical representation of different activities in the timeline.

The Program Evaluation Review Technique breaks down the whole activities in individual tasks of a project for analysis purposes.

PERT charts are considered to the Gantt bar chart. because they are identified task dependencies, but they are often more difficult to interpret the activity and event. Which was developed in 1950.

It helps a project manager, to analyze a project’s various tasks and estimate the amount of time required to complete each task in the project activities.

Using this subjective information, the project manager can easily estimate/ calculate the minimum amount of time required to complete the whole project activity.

This information also helps in a budget and to determine all types of resources needed to complete the project.

PERT is followed the Probability approach. it calculates the three-time estimation for activity.

Read More: 10 Free Construction Estimating Software

Advantage Of CPM

  • CPM indicates the activities that can run parallel to each other. It is easily found out the most critical elements of the project.
  • CPM gives a practical base visualization that helps in determining how to reach the aim of the project within the time limit.
  • CPM is effective in new project management. It can strengthen a team’s perception if it is applied properly.
  • CPM provides a demonstration of dependent activities. CPM helps in the scheduling of individual activities. It shows the various project activities and their outcomes as a network diagram.
  • CPM gives a fair and parallel procedure of documenting of project. It helps in determining the slack time of the activities.
  • A clear-cut approach to communicating project plans, schedules, time, and it also developed cost performance.
  • CPM is mostly used in the construction industry. It helps in time optimization by determining the project duration.

Disadvantages Of CPM

  • In CPM, it is difficult to estimate the completion time of the activities.
  • The critical path is not always clear in the critical path method. when succeeding and preceding activities are more.
  • For larger projects, critical path method networks can be complicated too.
  • It also does not manage the scheduling of all types of resource allocation.
  • In the critical path method, a critical path needs to be calculated very accurately. Because that affects the completion time of the particular project.

Advantage Of PERT

  • PERT (Program Evaluation and Review Technique) is suitable for large types of projects. also, scheduling of different activities is done easily.
  • Each subordinate manager has to plan the events for which he or she is responsible. It’s the main focus on critical elements of the project. that may need correction.
  • It makes a forward-looking concept for the project manager.
  • The main aim of the PERT reports and pressure for action at the particular spot and particular organization level at the right time.

Disadvantages Of PERT

  • Another biggest disadvantage has been it gives time importance but not on costs.
  • It is more suitable for large and complex projects and not suitable for small and repetitive works.
  • Also, the time required to complete each activity is highly subjective, so the programmer evaluation review technique is a high chance of an incorrect critical path.

Read More: 12 Types of Estimate | Types of Estimation

Component Of CPM and PERT Network

In CPM and PERT networks involves following two major components,

  1. Activity
  2. Event

Activity: An activity shows action and utilization of resources such as money, time, and material required to complete the project.

  • Activity is represented by an arrow.
  • In the network two types of activities are there, Preceding and Succeeding activities.
  • Preceding Activity: Activities perform before a given event are called preceding activities
  • Succeeding Activity: Activities perform after a given event are called succeeding activities.

In figure activities A and B preceding activities C and D respectively. Where activities A and B are succeeding activities for Event J and K.

Event: An event will always occur at the beginning of the activity and end of the activity.

  • In-network numbering the evet applying Fulkerson’ RULE.The event has no resources.
  • Event is denoted by a node. A node may be shaped in a circle, square.
  • In the network, various types of events are there, namely Head event, tail event, merge and burst event.
  • In the above figure event I is Head event and J is Tail event for activity A. also L event is merged event and I is burst event.

Dummy activity: An imaginary activity that does not consume any time and resources is known as a Dummy activity.

  • Dummy activities are denoted by the Dotted line.
  • The main function of dummy activity is representing a connection between events to maintain the sequence logically.

Critical Path Analysis

The critical path for any network is the longest path of the whole project network. all the activities will be complete then complete the whole project.

if the project is to be completed in the shortest time, all activities on the critical path must be started as soon as possible. These activities are called critical activities.

Any delay in the critical activity will increase the project duration. Any type of delay considers here such as bad weather, accident, and some technical reason.

Project duration directly affects the budget of the project. activities do not lie on the critical path is known as non-critical activities.

These types of non-critical activities may have some slack. the slack is the amount of time by which the start of an activity may be delayed without affecting the entire completion time of the project.

But critical activities have no slack.to reduce the overall project time it would require more resources like man, material, machinery at extra cost to reduce the time taken by the critical activities to complete.

Example: How to Calculate Project Completion Time

A project schedule has the following data,

  • Construct PERT network.
  • Compute TE and TL for each activity.
  • Find the critical path.

From the given data, the activities network are constructed as shown in the figure below

What Is PERT and CPM | Difference Between PERT and CPM | PERT and CPM Example
Difference Between PERT and CPM: Full Form 5

To determine the critical path, compute the earliest time TE and latest time TL for each of the projects. The calculation of TE and TL are as follows,

To calculate TE for all activities

  • TE 1 = 0
  • TE 2 = TE1 + t1,2 = 0+4 = 4
  • TE3 = TE1 + t1, 3 = 0+1 = 1
  • TE4 = max (TE2 +t2, 4 and TE3 +t3,4)
  • TE4= max (4 + 1 and 1+ 1)
  • TE4= 5 Days
  • TE5 = TE3 + te3, 6 = 1+6 = 7
  • TE6 = TE5 + te6 = 7+4 = 11
  • TE7 =15
  • TE8 = 17
  • TE9 = 10

To calculate TL for all activities

  • TL10 = TE10 =22
  • TL9 = TE10 – t9,10 = 22 – 7 = 15
  • TL8 = TE10 – 18,10 = 22 – 5 = 17
  • TL7= TE8 – t7,8 = 17 – 2= 15
  • TL5 = 7
  • TL4 = 10
  • TL3 = 1
  • TL2 = 9
  • TL 1= 0

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