The Project Triangle or Iron Triangle expresses the Triple Constraint of time, cost and quality or scope that must be managed in project delivery. Each constraint is connected and moving one point of the triangle will impact the other two points. stakeholdermap.com

One of the first project management concepts that I learned was the Time, Cost, Quality Triangle. Also known as the Iron Triangle or Triple Constraint. I was given the task of managing a conference and I was trying to find a way to express a common challenge. The conference date was fixed and there simply wasn't enough time to write, design and print the completed full-color training materials by the start of the conference, thankfully the Project triangle came to my rescue.

The Iron Triangle of time, cost and scope or quality

In the mid 1980s Dr. Martin Barnes created the Triangle of objectives. The triangle demonstrates that quality cost and time are interrelated. Focussing or fixing one point of the triangle impacts the other two points (Lock, 2007, p21).

In other words if one part of the triangle is fixed the other two points have to move, so if quality is fixed, time and/or cost may need to increase.
In the case of the conference a trade off had to be made in quality or cost to meet the fixed date. In the end the printing was changed from color to black and white and drafts were sent to the first day of the conference with final versions arriving on the third day.

Dr. Barnes later updated the triangle to performance, cost and time as he felt that quality implied little more than compliance with specifications.

Dennis Lock points out that many more derivations of the triangle have since been developed (2007, p22). My perception is that the most often seen variation is to replace performance or quality with scope. In my opinion this is a calculated attempt to insist that compliance to specification is - as Barnes tried to avoid - all that is required. This is perhaps partly the cause of the common complaint that waterfall project management methods are inflexible, fix requirements and are resistant to change.

Common variations of the project triangle

How to use the Iron triangle

Decide at the start of a project which version of the triangle you will use and agree with the project sponsor which of the three or four objectives are most important.

Assess all changes, risks and issues against the triangle and weigh up your course of action against the impact on your critical objective. For example if the key project constraint is cost, only the most business critical change requests are likely to be approved. However, if quality is the biggest goal time and cost might move to accommodate enhancement requests.

Note on the history of the Triangle According to Andy Oppel some claim that the concept of three interrelated objectives comes from Hollywood where producers manage three interrelated objectives: aspiration of a quality film, produced quickly on small budget (2009).

Project triangle references

Office, 2014, The project triangle, [online] Available at: https://office.microsoft.com/en-gb/project-help/the-project-triangle-HA010351692.aspx [Accessed 19 November 2014]

Andy Oppel, 2009. Data Modeling: A Beginner's Guide by Oppel, Andy (2009) Paperback, McGraw-Hill.

Ralph L. Kliem, Irwin S. Ludin, Ken L. Robertson, 1997. Project Management Methodology: A Practical Guide for the Next Millennium: A Practical Guide for the Next Millennium, New York:CRC Press.

Dennis Lock, 2007. Project Management. , 9th ed. Aldershot:Gower Publishing Limited. Latest edition Project Management from Amazon.

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