Project Management Triangle

The Project Management Triangle is a model of the constraints of project management.

Like any human, undertaking projects need to be performed and delivered under certain constraints. Traditionally, these constraints have been listed as "scope," "time," and "cost".These are also referred to as the "Project Management Triangle". Where each triangle side represents a constraint, its to be noted that one side of the triangle cannot be changed without affecting the others.

   Time   : The time constraint refers to the amount of time available to complete a project. 
   Cost    : The cost constraint refers to the budgeted amount available for the project.
   Scope : The scope constraint refers to what must be done to produce the project's end result.

These three constraints are often competing constraints: 
  - Increased scope typically means increased time and increased cost.
  - A tight time constraint could mean increased costs and reduced scope
  - and a tight budget could mean increased time and reduced scope.

The discipline of Project Management is about providing the tools and techniques that enable the project team (not just the project manager) to organize their work to meet these constraints.

Time

For analytic purposes, the time required to produce a deliverable is estimated using several techniques. One method is to identify tasks needed to produce the deliverables documented in a work breakdown structure or WBS. The work effort for each task is estimated and those estimates are rolled up into the final deliverable estimate.

The tasks are also prioritized, dependencies between tasks are identified, and this information is documented in a project schedule. The dependencies between the tasks can affect the length of the overall project (dependency constrained), as can the availability of resources (resource constrained). Time is different from all other resources and cost categories.

Cost

To develop an approximation of a project cost depends on several variables including: resources, work packages such as labor rates and mitigating or controlling influencing factors that create cost variances.

Tools used in cost are, risk management, cost contingency, cost escalation, and indirect costs .

Scope

Requirements specified to achieve the end result. The overall definition of what the project is supposed to accomplish, and a specific description of what the end result should be or accomplish. 

A major component of scope is the quality of the final product. The amount of time put into individual tasks determines the overall quality of the project. Some tasks may require a given amount of time to complete adequately, but given more time could be completed exceptionally. Over the course of a large project, quality can have a significant impact on time and cost (or vice versa).

Together, these three constraints have given rise to the phrase "On Time, On Spec, On Budget." In this case, the term "scope" is substituted with "spec(ification)."