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Project Management: The 3-Legged Stool Concept Explained

Updated: Jun 2

What Is The 3-Legged Stool of Project Management?

In project management terms, the '3-legged stool' refers to the three critical aspects of a project that require careful management: scope, cost and time. The concept is that if there is an impact on one, it has a direct consequence on the other legs.

The 3 legged stool of project management diagram
The 3-legged stool of project management

The Impact of Changes in Scope, Time & Cost

For example, if you adjust the time available to your project and shorten it, you may need to either reduce the project's scope or increase the costs to bring in more resources, or maybe both.

Alternatively, if you increase scope, you'll likely have to adjust your timeline and costs.

It reminds project managers to monitor these aspects of their projects closely.

The same concept is often alternatively referred to as the "Project Management Triangle", as per the diagram below.

A fourth dimension of quality is sometimes added to the model, but it tends to remain fixed; as project outputs need to be of a certain quality, so there isn't usually any room to adjust that, which is why it sits in the middle of the above triangle.

If any of the other three aspects (or legs of the stool) can be adjusted, you will likely need to adjust the others to balance the stool.

A diagram showing the 3-legged stool and the components of a project
The project management triangle (3-legged stool)

What Are The Three Legs of Project Management?

The 3 legs are Scope, Cost and Time.

Below we'll explore each in more detail.

A picture of the word 'scope'


Scope in a project refers to the detailed set of deliverables or features of a project, including all work necessary to complete these deliverables successfully, outlining the boundaries and requirements of the project to ensure clear understanding and agreement among all stakeholders.

A well-defined scope is crucial for the success of any project, as it sets clear boundaries and expectations for the team and stakeholders. It's also been my experience that it's equally important to capture what is outside of scope, to ensure stakeholders don't make assumptions about what they are getting.

Managing scope can be challenging, as projects often tend to extend beyond their original objectives through something referred to as 'scope creep', which is the silent killer of many projects.

In my experience, scope creep is rarely obvious and tangible. It tends to sneak up on you, silently like a ninja ready to kill the project. By that, I mean large changes in project scope are much easier to identify and then manage through change management and normal project meetings, but the smaller changes tend to go under the radar and are much harder to detect, but they add up to huge impacts on your project's direction, timescales and costs.

In a software project, your product manager watches and controls the scope like a hawk (at least they should be!). However, it may often fall directly to the Project Manager to control the scope and ensure that changes are managed.

So, Project Managers need to devise a plan for effective scope management; otherwise, it will impact one of the other legs of the stool: time or cost, and escalations in either of these are rarely welcomed by project sponsors.

It's crucial to clearly detail the project’s size, complexity, and objectives from the outset. This plan serves as a roadmap for the project team, helping them stay on track and ensuring that all project deliverables are aligned with the project’s objectives. It's okay to have changes to scope and requirements, but how they are managed alongside other commitments and priorities makes the difference to project success.

Recommendations for Managing Scope

Here are a couple of things you can do to manage the scope.

Clarify Scope At The Start of the Project with a Project Charter

I said earlier that it's important to document the scope and what is in and out earlier, but how can you do that? Well, I recommend creating a Project Charter or Project Initiation Document (PID). They are pretty much the same, with the PID being the PRINCE2 version of a Charter.

The Charter helps you clarify exactly what the project delivers in black and white. It's not going to go through every requirement in detail (or it may, depending upon the nature of your project), but it will focus stakeholders on what the project is delivering and the major anticipated outcomes that should result in the project's success. If completed collectively with stakeholders, you'll find it useful to facilitate discussion.

A little robust discussion right up the front of the project about the scope is far better than outright arguments and major adjustments to the scope at the far end of the project.

Establish a Robust Change Management Process

The next way to approach scope changes in a project and manage the impact on the other legs of the project management stool is to implement a Change Management Process.

Now, it will depend upon the style of your project as to how you manage change. For example, if you are delivering to an external customer for a fixed cost, you might have a clearly documented process that ensures any change (known as a Request for Change, or RFC) is evaluated. It might, for example, lead to additional costs or an extended timeline. But, a process to evaluate change and its impact is crucial, regardless of how you carry it out.

Using a Backlog to Control the Scope

Another method to managing scope and its impact is found in an approach called 'Agile'.

Agile is typically, but not exclusively, used in software delivery, where requirements come in thick and fast as the software is being developed. Therefore, they usually maintain a 'backlog' (or list) of requirements, which are constantly 'groomed', estimated and prioritised.

Delivery is often broken into cycles, picking up, for example, the top three things on the list and delivering them over two weeks, and then picking up the next three deliverables. This gives the project much more control over scope, as items can always be added and reprioritised. Then the timeline and cost legs can usually be maintained, but the scope adjusted to fit.

The word 'costs'


Another vital component of project management is cost management, which encompasses the financial resources for the project.

Time equates to money, and if there is a change in one, it typically directly impacts the other. A reduction in time, may necessitate an increase in resources.

Types of Costs

I was taught a mnemonic device that stuck with me for making sure you are thinking of all aspects of your budget; "THE SPA" stands for "Transfer, Hardware, External, Software, People and Accommodation".

Looking at each of these can help you build a rounded budget and lessen the chance of overlooking something big.

  • Transfer Costs

  • Hardware Costs

  • External Costs

  • Software Costs

  • People Costs

  • Accommodation Costs

CapEx & OpEx

In the context of business management and budgeting, the two critical types of expenses are CapEx (Capital Expenditure) and OpEx (Operational Expenditure).

CapEx (Capital Expenditure)

CapEx refers to the funds a company uses to acquire, upgrade, and maintain physical assets such as property, buildings, technology, or equipment.

These are typically large investments in assets that will benefit the business over a long period.

Capital expenditures often involve a significant amount of money and are usually invested in projects or assets that have long-term benefits. These costs are capitalized for accounting purposes, meaning they are not expensed fully in the year they are incurred but are depreciated or amortised over their useful life.

Examples might include purchasing new equipment, upgrading a computer network, building a new factory, or acquiring a new building.

OpEx (Operational Expenditure)

OpEx, however, covers the costs associated with the day-to-day operations of a business.

These expenses are necessary for the ongoing functional aspects of a company.

Operational expenditures are usually shorter-term costs and are fully expensed in the accounting period they are incurred. They are essential for the management and maintenance of current business operations.

Examples include salaries and wages, rent for office space, utility bills, maintenance and repairs, and costs of goods sold.

Managing a Project Budget

Here are some pieces of hard-won advice for when it comes to managing budgets for projects and lessening the impact on your scope or timescales.

Get Support

The larger your project budget, the more you will need support and oversight from specialists, i.e. the finance team or an accountant. They will provide a level of scrutiny and support that you might not have if you, like me, are an enthusiastic amateur in financial management. So, if you have access to such resources, I strongly recommend you grab it with both hands!

It needn't be complicated. On a recent project with a budget of about $2.5m I met with the workstream leads and the CFO once a month to review the costs and see if anything had materially changed.

A zero figure is (almost) always wrong - Nothing costs nothing, and absent estimates are dangerous.

What I mean by this is that there is a temptation by many not to put in estimates for certain parts of your project because they haven't yet investigated or had quotations, etc. But if you put a figure of zero into your spreadsheet for these, then it is 100% guaranteed to be wrong, therefore it is always better to put something in than nothing.

Cashflow is critical.

The larger your project, the more important it is to recognise when costs will be taken from the bank account. So, when you create a budget, you should do so recognising when payments are needed. You're Finance Director, VP, Manager, CFO, Controller, call them what you will, is not going to be happy if you rock up on a Thursday afternoon and say, 'Ok, it's time to pay that 100k that we spoke about!'. They need to predict high levels of spending along with incoming funding and other commitments. It could, in a worst-case scenario, even derail the company's cash flow.

This leads us back to item #1 - work with finance representatives to make sure there are no 'gotchas'.

I've created a template for tracking costs, which I've used over the years several times. Feel free to download it.

The word 'time'.


Time is what we tend to think of when we think about project management. Or at least, it's what others think of when discussing projects. "Can you deliver it on time?" or "How long will it take?"

These are crucial questions but are only an aspect of managing a project.

Managing time in project management is akin to steering a ship through a maze of icebergs. It requires precision, foresight, and the ability to adjust course as needed. Here are a few strategies to help navigate these waters.

Develop a Detailed Project Schedule

The cornerstone of effective time management within a project is the development of a detailed project schedule. This is not merely a to-do list but a comprehensive plan that aligns project activities with project milestones and deadlines. Tools such as Gantt charts or project management software can be instrumental in visualising the project timeline and dependencies between tasks.

Creating a project schedule involves breaking the project into smaller, manageable tasks, estimating the duration for each task, and identifying dependencies. This process, often called work breakdown structure (WBS), ensures that every aspect of the project is accounted for and scheduled.

Implement Time Tracking Mechanisms

To manage time effectively, knowing how it's being spent is essential. Implementing time-tracking mechanisms allows you to monitor the actual time spent on project tasks compared to the estimated durations. This real-time data can be invaluable in identifying tasks that are taking longer than anticipated, enabling proactive adjustments to the schedule or allocation of resources.

Time tracking tools vary from simple timesheets to sophisticated software that can track time automatically and provide detailed reports. The key is to choose a system that fits your project's complexity and your team's working style.

Adopt a Flexible Approach to Project Management

Flexibility is a critical component of time management in project management. While a detailed schedule is vital, rigidity can be a project's downfall. Adopting a flexible approach, such as Agile project management, allows for adjustments to the project timeline based on real-time feedback and changes in project scope or resources.

In Agile methodologies, projects are divided into short sprints, and time is allocated for regular reviews and adjustments. This approach ensures that the project adapts to changes quickly and efficiently without significantly disrupting the timeline.

Conduct Regular Progress Reviews

Regular progress reviews are essential to ensure that the project remains on track. These reviews provide an opportunity to assess the progress against the project schedule, identify any delays or issues, and implement corrective actions promptly.

Progress reviews should involve key stakeholders and project team members, facilitating open communication and collaboration. They serve to monitor time and reassess priorities and resource allocations, ensuring that the project's objectives are met within the allocated timeframe.

Balancing the 3-Legged Stool of Your Project

The metaphor of the three-legged stool in project management—comprising scope, time, and cost—illustrates the necessity of balance to prevent the project from toppling over. Achieving equilibrium among these three elements can be challenging, but it is essential for successfully delivering a project. Here are several approaches to maintaining this critical balance:

Embrace Integrated Change Control

Integrated change control is a process that assesses the impact of any change across scope, time, and cost. It ensures that adjustments in one area do not adversely affect the others without consideration and approval.

By employing integrated change control, project managers can evaluate proposed changes comprehensively, determining how alterations in scope might necessitate adjustments in timeline or budget, and vice versa. This holistic approach ensures decisions are made with a full understanding of their implications on the project's overall balance.

Utilise Robust Project Management Tools

Advanced project management software can be an invaluable ally in balancing the three elements. These tools allow for the real-time tracking of project progress against the plan, facilitating immediate visibility into how changes in one area affect the others. Features such as Gantt charts, resource allocation graphs, and budget tracking can help project managers to anticipate problems before they arise and to re-balance the stool as necessary.

Foster Open Communication and Stakeholder Engagement

Open lines of communication with stakeholders and team members can significantly aid in maintaining balance. Regular meetings, updates, and feedback sessions ensure that all parties are aware of the project's status and any potential issues. Engaging stakeholders in discussions about scope, time, and cost can also help to manage expectations and to secure their buy-in for any necessary adjustments.

Implement Agile Methodologies

Agile methodologies, such as Scrum, are designed to handle change effectively, making them particularly useful for balancing the three-legged stool. By breaking down the project into smaller, manageable increments (sprints), teams can focus on delivering value while maintaining flexibility in scope, time, and cost. Regular sprint reviews and retrospectives allow for the continuous rebalancing of priorities based on project progress and stakeholder feedback.

Prioritise and Plan for Contingencies

Prioritising project requirements and tasks based on their value and impact allows for a more effective allocation of time and resources. Additionally, planning for contingencies by allocating reserve time and budget can provide a buffer for unexpected changes. This proactive approach enables project managers to adjust plans without sacrificing the project's overall objectives.

Continuously Monitor and Adjust

Continuous monitoring of project performance against the baseline plan is crucial. By closely monitoring metrics and indicators for scope, time, and cost, project managers can identify trends that may signal the need for rebalancing. Regularly revisiting the project plan and adjusting to new information or challenges ensures that the project remains aligned with its goals.

An image of a person balancing between 3 pillars


In conclusion, the concept of the project management 3-legged stool – scope, cost, and time – serves as a fundamental guide to balancing the critical elements of a project.

While adding quality as a central theme underscores its importance, the key to successful project management lies in adapting and managing these interconnected aspects effectively.

By employing these strategies and remaining vigilant about the dynamic nature of projects, you can navigate the complexities of project management and lead your projects to successful completion.

A successful balance of the project management’s three pillars necessitates a blend of strategies, such as prioritizing project goals, ensuring effective communication and collaboration, and adapting to change.

These strategies are crucial for navigating the complex world of project management, as they enable project managers to maintain equilibrium among scope, cost, and quality while also addressing the unique challenges that each project presents.

In the following sections, we will delve deeper into each of these strategies, exploring how they can be applied to effectively balance the three-legged stool of project management and achieve project success.

By understanding and implementing these strategies, project managers can ensure that their projects run smoothly, stay on track, and ultimately deliver the desired outcomes.

Here's another perspective on the 3-legged stool, or as presented in this video the 'Triple Constraint'.


About the Author: Alan Parker is a seasoned IT professional with over 30 years of experience in the industry. He holds a Degree in Information Systems and is certified in ITIL and PRINCE2. Alan has managed diverse IT teams, implemented key processes, and delivered successful projects across various organisations. Since 2016, he has been a sought-after consultant in IT governance and project management. Alan excels in simplifying complex problems and avoiding common pitfalls in IT management. Learn more about his journey and expertise here.


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