The project management triangle is a model in project management that shows how the balance between three constraints—scope, time, and budget—affects the quality of the project. The triangle shows that affecting one constraint will mean adjusting one or both of the others in order to maintain the quality. It’s also called the triple constraint model or the iron triangle. Project managers must oversee all three of these constraints in order to complete a project successfully.
Let’s say that you need to expand the scope of a project. This might mean extending the original schedule of the project, or increasing the budget in order not to affect the quality of the output. Likewise, shortening the schedule to meet an earlier deadline might mean increasing the budget or tightening the scope. Need to absolutely reduce the budget and timeline without changing the scope? Then the triangle might have to shrink—meaning the quality of the product might be reduced.
Scope: Scope refers to the deliverables and tasks that must be completed to achieve the project’s goals. The scope might change if stakeholders decide mid-project that they want to adjust a product, or add another product entirely.
Cost: Project cost is the total amount of money required to complete a project. This is also called the budget. Costs might include salaries for employees, and money for equipment, tools, office space, and other resources. Adding new members to a team or increasing the time it takes to complete a project can impact cost.
Time: Time is how long it takes to complete tasks in a project, and the project itself. This constraint is also called the schedule. An expanded scope can increase timelines. So can a decreased budget—for example, if a team member is removed from the team due to budget constraints, it can take longer to complete a project.
Some models show an enhanced project management “triangle” with six constraints. The six-constraint model adds benefit (sometimes replaced by “resources”), risk, and quality as three more separate constraints . This model is sometimes depicted as a six-point star made from two overlapping triangles.
The project management triangle is a useful concept for project managers for the following reasons:
It helps to see how changing one project constraint will affect other constraints. If you change the scope of a product you’re hoping to launch, you know that either the budget needs to increase, or the timeline needs to be extended (or both).
It can help mitigate risks. Say your project to launch a new piece of software has a hard deadline, and you’re worried your engineers will fall behind. You can ask stakeholders for a contingency budget, just in case you need to hire another engineer to help complete tasks.
It can clarify priorities in a project. Does your project have a hard deadline, a strict budget, or very specific deliverable requirements? Knowing this can give you a better idea of what a successful project will look like.
Here are concrete ways you can balance the constraints of the project management triangle.
Communicate with stakeholders: Speak with stakeholders to know what is acceptable change and which constraints should be prioritized. Is the deadline immovable or the budget strict? This will give you an idea of how the project can adapt should changes become necessary. This is a crucial step in the initial stages of the project, but frequent communication should happen throughout the project as well.
Establish risk management processes: Planning for risks should be a step baked into your project management process to prevent scope creep and stay within budget and on schedule. Identify risks, then establish a plan to mitigate each. If you’re looking for more detail, read about how to manage project risks.
Create change management processes: Change is often inevitable. Having a change management process in place creates a structured way for changes to be approved or rejected. This ensures the team is aware of changes as they happen and how they impact the project. This can also reduce scope creep.
Choose a methodology based on constraints: You might opt to adopt a project management methodology based on the constraints you face. Projects that face strict constraints are often managed through Waterfall-type approaches. If you need more flexibility, an Agile method like Scrum might be more fitting. Projects where inefficiencies need to be minimized as much as possible can benefit from a Lean approach.
Read more: 12 Project Management Methodologies: Your Guide
Mastering the project management triangle is one of the many fundamental concepts aspiring project managers should have under their belt. If you’re looking for a place to learn other essentials of project management, check out the Google Project Management: Professional Certificate.
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The project management triangle helps to illustrate the relationship between project constraints. It can also help reduce project risk, or provide insight into how to deal with them if they happen. The project management triangle can also help establish what the priorities are in a project.
The project management lifecycle has four stages: initiating, planning, executing, and closing. Some resources list five phases, adding “monitoring and controlling” to this list.
Scope creep can be caused by many factors. These include poorly defined scope, lack of communication between stakeholders and the team, unclear priorities, too many dependencies, and others.
Project Management Institute. "Six (yes six!) constraints: An enhanced model for project control, https://www.pmi.org/learning/library/six-constraints-enhanced-model-project-control-7294." Accessed September 15, 2021.
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