Iron triangle

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The Iron Triangle for project management, also called The Magic Triangle or The Project Triangle, is a tool illustrating the ground pillars when carrying out a project; time, cost and quality (TCQ). Traditionally, a project has been perceived as a success, when being able to deliver within time, cost and quality. The definition and formulation of the model and its ground pillars change according to sources. In some models, a fourth pillar is included, the Scope [1] [2] . This will be discussed in the article. When aiming for a successful project it would be optimal if there were no restrictions to especially the period and economical aspect, to deliver the highest quality when ending the project. However, all projects operate within constraints set to fulfil the overall given task. The Iron Triangle demonstrates the dependence of the ground pillars, as they are dependent resources with a pin-point approximation of the focus of the project. The triangle is an overall simple model to positioning the project between the three different variables all important to consider when aiming for a good final result. The usage of the Iron Triangle can be defined as the quote express;

The goal of the model is to maintain the focus of the triple constraint power structure on the project higher purpose.[3] .

The model is used in project management to plan and deliver a project. However, many projects do not success within the constraints set for time, budget and quality. Thus, the limits are often exceeded [4]. All projects are unique and complex and must be managed individually [1]. Thus, the model has limitations as a project’s success cannot be managed by only three boundaries, but the Iron Triangle can be used as guideline concerning project management [5].

This article will present the definition of the three ground pillars, their dependence and the application of the model in project management. As a conclusion on the article, the limitations of the model will be presented.


Big idea

The Iron Triangle is a model based on three constraints, time, cost and quality, which create a frame for project management and a path towards a successful result. In project management time and cost are highly dependent and linked directly to handling and planning a project. The quality aspect of the model is more discussed, and over time the third factor has been replaced by Scope, Performance, or Requirements. However, the model often returns to its original form as TCQ. The links between time, cost and quality has been identified as strong and decidedly connected contrary Scope, Performance, or Requirements. The three constraints have been commonly acknowledged as a success criteria and tool in project management. However, a large amount of literature [6] specify that there are many factors affecting the conclusion of success of a project whilst other elements affect the success of the management. This will be discussed further down.

The Iron Triangle is usually illustrated with the three ground pillars at each vertices of the triangle, as illustrated in the figure below. Some editions of the model have positioned Scope in the middle as illustrated in the second figure. The three ground pillars all contribute to the boundaries of the tasks towards the scope.

The Iron Triangle, to the left, with the three ground pillars. To the right, the Iron Triangle with a fourth pillar. Drawing: Emilie Winther Schmidt


The time is the plan, schedule and the deadlines operating as boundaries for the project. All projects must be delivered within a timeframe, and it must be evaluated whether it is realistic to deliver a task in the define time. If the time is being shortening, the quality is decreased, and the cost must raise to reach the proposed scope [2] . The desire about time, is to have the shortest project as possible. The timetable will often be reconsidered many times during a project. Deadlines will be exposed and new will emerge.


The cost is the budget and the resources used throughout the project. A project must be reasonable, thus an estimation of budget, needed resources and human hours are executed. Many uncertainties can affect the cost of the project, which often leads to overspending. However, occasions for lowering the cost can likewise appear. Though, if the cost is lowered, the quality is decreased, whilst the time must increase to reach the intended scope [2] . All project managers appeal to execute the cheapest project as possible. The cost can be redefined throughout the project.


The quality stands for the value of the result at the end of the project. The quality is measured by defined requirements. When aiming for a better quality than the intentional both time and cost must increase [2] . All project managers want to achieve the premier level of quality as possible. However, this must not exceed the requirements from the customer. The overall quality of the project and the final result can first be evaluated when the project is ended. The opinion on the quality can be individual and is not always as easy to measure as the two other constraints in the triangle [6].


The scope refers to the goal of the project and what accurately the project must provide. However, it can be challenging to place the project’s scope in the Iron Triangle due to the various of stakeholders’ desires. Customers, users and project managers often have different perception. Thus, if the transparency of the scope is not equal to all of the stakeholders, the project can be delivered on the wrong basis [2] .

Quality priority project positioned in the Iron Triangle. Drawing: Emilie Winther Schmidt
Cost and Quality priority project positioned in the Iron Triangle. Drawing: Emilie Winther Schmidt

The ground pillars

The three pillars are dependent on each other, but also very conflicting [3]. An example is, if the cost of the total project is low it will affect the time being used on the project as well as the quality of the final delivery. Not all three constraints can be as low/best as possible. Furthermore, when adjusting one of the of the pillars it will affect the other two, if not to expand the bounds. Today projects should be delivered within a short timeframe, at a tight budget and thereby with cheap resources and still deliver an acceptable product [1]. In this example the project would be placed between the cost and time in the Iron Triangle. This illustrates the conflict between the opposite constraints, where the project manager and the customer must decide on which factor is the most important.

It seems that the dependency between the three ground pillars increases when the project is complex and unmanaged uncertainties occurs. Therefore, a prioritising must be executed to be able to run the project.

The project is often placed in the triangle with a symbol to illustrate its prioritising. The project can be positioned in one of the corners, if one factor is more determining than others, or closer to the middle, where all factors are balanced. However, no project must be placed in the middle, as this will overcomplicate the project and make it unnecessarily difficult to make a decision. When managing a large project, it can be efficient to choose one or two of the pillars as the leading one with the highest priority. Thus, when new aspects and uncertainties appear it is easy to decide on the forward path for the project. An example is, if the project is depending highly on adhere to the budget and challenges arise, then the time must be expanded and/or the quality of the intended result must be inferior. Showed in the illustration, the project is placed close to the quality corner in the Iron Triangle. As a consequence of the quality priority project, the cost is high, and time is long. If the project is two pillar prioritised it is as illustrated in the figure beside. Then quality and cost are the demanding constraints. If the quality must be high and the budget low, then the time must expand significantly [2] .

In some cases, it might be obvious to position the project in the Iron Triangle. If the project must contribute to a bigger project with a deadline, then it is time dependent. An example could be a project delivering a result to the Olympic Games, where the start date is locked. Another example can be a organisation releasing a new medical device. Here the deadline is also very important, as they want to be the first on the market as well as market leaders. Furthermore, they cannot compromise on the quality as it is a medical device. Then the project is time and quality prioritised. Thereby, the only boundary the organisation can adjust is the total cost of the project. If problems occur the budget must be enlarged. This will cause a lower final profit for the organisation, if they are not able to raise the price on the absolute product.

Even though, the quality might tell something about the final result. This tool is mainly focusing on the project process. It communicates the success of the process carried out, but very little of the final result’s further path. The Iron Triangle cannot be used to measure the benefits or the user satisfaction. Thus, it is important to use this tool along other management tools to create a fully successful process and result [7].

The Iron Triangle is a commonly used tool when managing a project for many decades. However, modifications of the Iron Triangle have been developed. A new version of the tool contains six pillars, whilst others have added a third dimension to the triangle, where softer and less measurable aspects are present, e.g. value for customer, value for the project team etc.


The Iron Triangle is used for project management, when a project has a defined start and end. Project management is utilising a gathering of models, tools and techniques to move a unique project forward [5].

The Iron Triangle is originally used in the beginning of a project to estimate the three factors and concrete the boundaries for the project. Ideally, the model must be recreated multiple times through the project, as the boundaries change. The Iron Triangle is simple, and it is easy to identify whether the project has been delivered within the success criteria set, and otherwise the project management success can be declined. The project itself might still provide its purpose or create value for the customer and user even though the project management has not been an accomplishment according to the Iron Triangle. This means that there must be distinguished between a project’s success and the success of the management of the project. In this relation, the Iron Triangle measure the achievement of the management more than the final outcome [6].

Given a project with restricted time, the project manager must look into the dependence of the three pillars. The project manager will schedule the project within the timeframe. Quality of the output is always dependent on the time and budget available. Thus, the project manager must guarantee enough resources to reach the quality and scope in time. This will automatically raise the cost. The example illustrates that the project manager must compromise on whether cost or quality to deliver the project to the deadline. This might be a simple task to do when defining the project. However, uncertainties can appear, which displaces the project in the triangle concerning the boundaries. Furthermore, there is a naturally limit of all constraints. Therefore, the time, cost or quality cannot be infinite expanded or lowered [1].

Project management is driven by the benefits, planning, delivering and controlling the risk and the project within the boundaries identified for time, cost, quality and scope. This way the project manager can measure the success of the project management if it is executed right regarding the estimations in the Iron Triangle. If the project works within a programme, the project must also accomplish the requirements set within the sample of projects. In relation to this, the projects’ ground pillars can also be controlled by the overall programme management, where the success is determined on foundation of whether it was the correct project to carry out. Thus, if the project also delivers benefits for the organisation. The programme can be a part of a portfolio, which has an overall strategy. The time, cost, quality and scope must therefore operate within this, e.g. growth of profitability, reach the Sustainable Development Goals etc. [1] [2] .

All first estimations of the Iron Triangle must be reconsidered through the project. Estimations are often too optimistic. Thus, many projects fail to deliver within the frame set in the beginning. Furthermore, the business strategy or the stakeholders’ needs can change during the project. The primary focus on the model changes over time as the project is moving regardless of the priorities and requirements set. In the beginning of a project the time is often the most important one. If the quality is the most important requirement and the time and cost are decided according to this, the time will still be in the primary position when beginning the project. The schedule is in focus in the beginning, needed to start the tasks. It is defined how long the project will take place and milestones are outlined. Through the project the cost will have the primary focus, determining how appearing challenges will be handled. It needs to be decided what can be carried out based on the cost. All this with the final result in mind. When a project has ended, the quality will be in focus, and the success of the process and result will be determined [4] [1] [3]. Along with constantly changing the model, it is crucial to communicate with the important stakeholders. The project cannot be placed in the triangle without a defined strategy for the overall project and the organisation. The project manager must ensure to inform all stakeholders and make sure that they have agreed on the right basis. The strategy must be discussed with the stakeholders, often being the customer and users. However, the stakeholders might not always know what they want or what they actually need. Thus, the project manager must be ready to change the scope and the boundaries. Change in scope will increase time or cost. Thereby, there must be a certain flexibility of the position in the Iron Triangle. This way the project manager can ensure that the final result will live up to the different stakeholders’ desires. Otherwise the project can easily get off road and end up being unsuccessful, as the quote from the PMI Standard A Guide to the Project Management Body of Knowledge states:

The project team needs to be able to assess the project situation, balance the demands, and maintain proactive communication with stakeholders in order to deliver a successful project.[1].


The Iron Triangle is developed for over 70 years ago to successfully deliver a project. However, many projects still fail, and the model has become incomplete when looking at the way projects are managed today [5]. More than half of projects carried out are delayed, expand the budget and/or the final results are predicted incorrect [4]. Misunderstanding or misapprehending of the Iron Triangle will result in the project fails even though the project management were successful at other aspects of the total project [6] . All projects are unique, thus a selection of tools in a broad toolbox is needed as all projects must be managed individually.

The Iron Triangle is developed based on theory and was later implemented practical. When exploring the tool in project management, an emergent acknowledgement of the consequence of stakeholder relationships and influence arose. The success is thereby not only determined by the three constraints, time, cost and quality, but the stakeholders’ perception of a successful project and expatiations to the project are important as well [3]. Thus, the Iron Triangle is an unfinished model that simplifies the path towards a final project [5] [6], as there are many factors affecting and controlling a project. The success of a project will also be evaluated based on the less task related factors as the benefits for the customer and end-user. Along with this, a project will always exist in a context defined by laws and regulations, business strategies, the stakeholders’ needs and a demand for creating or improving something. Furthermore, individual motivation and communication in team is important to execute a positive project outcome [1]. It is an advantage if projects fulfil the requirements set for budget, time and quality, but first of all the project must add the intended value for the customer and/or user. Along with this, it is unmanageable to control the complexity of a project only through the three pillars, as risk is a large part of project management. Uncertainties through the project will affect especially time and cost. The Iron Triangle do not illustrate the complexity of the project and challenges regarding change of scope, appearing uncertainties etc. [2] [6].

The Iron Triangle is a good measurable tool to delegate task and prioritise multiple factors. However, good management of projects is more than delivering within the time, cost and quality. The importance of benefits and risks is just as important and determining. The Iron Triangle can help to determine the success of the management of the project but has become incomplete regarding the success of the actual project.

Annotated bibliography

Maylor, H., (2010): Project management, Chapter 4

The book has a description of the Iron Triangle with great examples of real projects executed. In chapter 4, it is explained how a project can be placed in the triangle, and what the position means for the process. Furthermore, it describes the three pillars, their benefits in project management and their limitations. It is discussed when it is useful to involve the model and phases of projects where it makes less sense. Furthermore, it describes the Iron Triangles relation to an organisation’s strategy and how it is desired to deliver a project as fast and cheap as possible with a high quality.

Caccamese, A. & Bragantini, D. (2012): Beyond the iron triangle: year zero, Paper presented at PMI® Global Congress 2012—EMEA, Marsailles, France. Newtown Square, PA: Project Management Institute,

This paper explains how the Iron Triangle is traditionally used, but it is focusing on the limitations of the model, as the three ground pillars are not enough to determine on the success of a project or management. It communicates the need for softer factors, which are less measurable. It discusses why it is an advantageous to expand the model with more corners or dimensions. Additionally, the definition of successful projects and management of projects are defined according to the PMI Standard. This is also described in relation to the project, programme and portfolio management.


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 P.M.I. (2017): A Guide to the Project Management Body of Knowledge, 6th edition, Project Management Institute
  2. 2.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 AXELOS (2017): Managing Successful Projects with PRINCE2, 2017 Edition, The Stationery Office Ltd, 2017. ProQuest Ebook Central,
  3. 3.0 3.1 3.2 3.3 Van Wyngaard, C., Pretorius, J. and Pretorius, L. (2012): Theory of the Triple Constraint – A Conceptual Review, Proceedings of the 2012 IEEE International Conference on Industrial Engineering and Engineering Management, IEEE Conference Publications: 1991-1997
  4. 4.0 4.1 4.2 Flybjerg, B. (2011): Over Budget, Over Time, Over and Over Again, From Peter W. G., Morris, Jeffery K. Pinto, and Jones Söderlund (2011): The Oxford Handbook of Project Management (Oxford University Press.), pp. 321-344
  5. 5.0 5.1 5.2 5.3 Atkinson, R. (1999): Project management: cost, time and quality, two best guesses and a phenomenon, its time to accept other success criteria, International Journal of Project Management, DOI:10.1016/S0263-7863(98)00069-6
  6. 6.0 6.1 6.2 6.3 6.4 6.5 Pollack, J., Helm, J. & Adler, D. (2018): What is the Iron Triangle, and how has it changed? International Journal of Managing Projects in Business, 11(2), 527-547.
  7. Pinto, M. and Pinto, J. (1991): Determinants of cross-functional cooperation in the project implementation Process, Project Management Journal, 20(4): 15–20
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