14 Difference Between CPM and PERT | What Is CPM | What Is PERT


The network technique is a major advance in management science.

This technique is based on the basic characteristics of all projects, that all work must be done in well-defined steps. For example, for completing a foundation, the various steps are (1) Layout, (ii) Digging, (iii) Placing Sideboards, and (iv) Concreting.

The network technique exploits this characteristic by representing the steps of the project objective graphically in the form of a network or arrow diagram.

It would be difficult to find in the history of management methods any technique which has received such widespread attention as that accorded to network methods for planning, scheduling, and controlling.

The network techniques are called by various names such as PERT, CPM, UNETICS, LESS, TOPS, and SCANS. However, these and other systems have emerged from the following two major network system:

  1. CPM
  2. PERT

What Is CPM?

Critical Path Method

Critical Path Method

CPM Full name Critical Path Method

Critical Path Method (CPM) is an effective tool for scheduling the activities of a complex Project. It was developed by Morgan R. Walker of DuPont and James E. Kelley Jr. of Remington in 1950.

In CPM networks, the entire project consists of a number of clearly recognizable operations or jobs, called activities. Activities are usually operations that take time to carry out, and on which resources are an expense.

Junctions between activities are term as events. The CPM net-works are often referred to as activity-oriented diagrams in which an arrow represents each activity, and the sequence of the arrows shows the sequence in which the activities are performed.

For example, at a foundation construction project, the various activities may be; layout the foundation trench’, ‘excavate the foundation,’ ‘put sideboards,’ ‘concrete the foundation base,’ etc.

CPM network is generally used for repetitive kind projects, or for those projects for which a quite accurate estimate of time for completion of each activity may be made; and for which cost estimations may be made using a fair degree of accuracy.

For example, CPM is very helpful for construction projects. But it isn’t suitable for development and research projects.

Also, read:Methods of Design | Difference Between Working Stress Method and Limit State Method

CPM Basic Steps:

  • Determine the required tasks
  • List required tasks in sequence
  • Create a flowchart including each required task
  • Identify all critical and non-critical relationships (paths) among the required tasks
  • Assign an expected completion/execution time for each required task
  • Study all critical relationships to determine all possible alternatives or backups for as many as possible

Also, read: What Is Building Bye-Laws

What Is PERT?

Program Evaluation Review Technique

Program Evaluation Review Technique 

PERT full name Program Evaluation Review Technique 

This PERT method First developed by the United States Navy in 1958, is commonly used in conjunction with the critical path method in the year 1957 (CPM).

The method was developed from the Navy Special Projects Office at co-operation with Booz, Allen, and Hamilton, a management consulting firm, also Lockheed Missile System Division for assessing the feasibility of existing schedules on Polaris missile program and for reporting progress.

The PERT system uses a network diagram consisting of pf events that have to be established to reach project objectives. An event is that particular instant of time where some specific part of a plan is to be achieved.

It indicates a point in time and does not require any resources. PERT uses event-oriented network diagrams in which arrows join successive events.

For example, at a foundation construction project, the various events could be’foundation layout started,” foundation excavated,” sideboards fixed,” concreting completed’ etc.

The approach of event-orientation in the network diagram grew out of the desire to report on the project progress via discernible management milestones.

Also, read: Trapezoidal Footing Formula with Calculation

PERT Basic Steps:

  • Identifying Tasks and Milestones: Each project involves a series of required tasks. These tasks are listed in a table, permitting additional information on timing and sequence to be added later.
  • Placing the Tasks at a Proper Sequence: The tasks Have Been Examined and placed in a sequence to get the desired results.
  • Network Diagramming: A network diagram is drawn with the activity sequence data showing the sequence of concurrent and sequential activities.
  • Time Estimating: Here Can Be the time required to carry out each activity, in three parts:
    • Optimistic timing: The shortest time to complete an activity
    • Most likely timing: The completion time having the highest probability
    • Pessimistic timing: The longest time to complete an activity
  • Critical Path Estimating: This determines the entire time required to complete a project.

Also, read: Methods of Design | Difference Between Working Stress Method and Limit State Method


CPM & Pert

1 CPM full name Critical Path Method PERT full name Program Evaluation Review Technique
2 PERT is that technique of project management which is used to manage uncertain (i.e., time is not known) activities of any project. CPM is that technique of project management which is used to manage only certain (i.e., time is known) activities of any project.
3 The CPM is a statistical technique of project management this is managed well-defined activities of a project. The PERT is a project management technique, used to manage uncertain activities of a project.
4 This CPM is a method to control cost and time. The PERT is a technique of planning and control of time.
5 CPM Method orientation like Activity-oriented PERT Method orientation like Event-oriented
6 In CPM method evaluation of Evolved as Construction project In this method evaluation of Evolved as a Research & Development project
7 Model type Deterministic Model type Probabilistic
8 In this method Focus on Time-cost trade-off In this method Focus on Time
9 CPM Method calculated estimates only one-time estimate Here, the PERT method estimates Three-time estimates
10 Appropriate for Reasonable time estimate Appropriate for High precision time estimate
11 Management of Predictable activities Management of Unpredictable Activities
12 Nature of jobs Repetitive nature Nature of jobs Non-repetitive nature
13 Critical and Non-critical activities is Differentiation Critical and Non-critical activities are No Differentiated
14 Use in Research and Development Project Use in Non-research projects like civil construction, shipbuilding etc.

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