Scope and the Triple Constraints of Quality-Time-Cost

We’ve all heard the old management joke about your project’s delivered scope: good, fast and cheap; you can pick only two. Experienced project managers chuckle at the joke but there is an underlying truth to it that all PMs cannot ignore.

Golden Triangle.jpg

On every project, there is an intrinsic relationship between Scope and the triple constraints of Quality, Time, and Cost. These combined four items are sometimes referred to as a project’s “golden triangle.” They are also known as the four “what’s” of a project: 1) What are you tasked with building; 2) What level of quality it needs to be built to; 3) What time frame do you have to deliver to; and, 4) What cost constraints are you to build within?

To better understand this the relationship between Scope and the Triple Constraints, let’s start with a general review of Scope:


In simple terms, Scope is what you and your project team are ultimately going to produce and deliver at the end of the project. It is sometimes called “the deliverable” of the project, and it includes all the various product bits and pieces, assembled together, and containing all the required features and functions that were defined and documented during the early phases of your project. Scope also requires all the supporting project functions and efforts required to organize, oversee, and support the development of the deliverable.

For instance, if you’re tasked with building a house, then the product scope is, well, the house itself. It might also include the purchase and inclusion of the land the house sits on, the furnishings that go into the house, additional outbuildings, and so on.

Further, the product scope definition from your customer or sponsor might also include specific features and functions they want included. For example, the scope definition might include a statement that says the house will have a minimum of three bedrooms and two baths, include separate living and family rooms, and have a detached 2-car garage with a covered walkway to the main house.

In other words, Scope is the high-level formal definition of the “what” that you’re going to deliver by the end of project. Simple, right?

Yes, but there are always constraints, or boundary conditions, that are placed on you when organizing and planning the delivery of the scope. In fact, there are three primary categories of these, and they’re often referred to in PM parlance as the “triple constraints,” or sometimes as the “golden triangle” of project management.

The Triple Constraints

Constraint #1: Quality

First and foremost of the three constraints is Quality. This is a term we use to define “how good” the scope must be.

Using our house example from above, the quality requirements placed on the scope might include such things as the type of tile used in the bathrooms, the specified exterior finish (e.g., brick or stucco), and the minimum acceptable lifetime of the roofing materials.

Quality defines exactly what it sounds like: i.e., the minimum acceptable standard of quality of the delivered scope. In other words, you can deliver a 3-bedroom, 2-bath house on one project that is constructed with significantly higher quality materials and furnishings than another 3-bedroom, 2-bath house that has an identical floor plan, volume and shape. Both of these projects have identical scope, but they have significantly different quality standards that must be adhered to.

Constraint #2: Time

The second major constraint placed on a project is that of Time (a.k.a. schedule).

Your customer and/or sponsor does not want to wait forever to have the product delivered. At a high-level, the schedule defines when you will in fact be required to make the final handover of the deliverable. At a lower level, the schedule also lays out other important dates and milestones that you might be required to hit along the way.

For example, the acquisition of the land for your house project, along the start of construction, may need to occur by the end of the current calendar year, because new zoning laws go into effect the following year. Or basic construction and “dry-in” of the building needs to be completed before a rainy winter season hits.

Other important dates, like beneficial occupancy and/or purchase of the furnishings are also often required by the customer, and are therefore included in the schedule constraints placed on you.

Constraint #3: Cost

The third constraint placed on a project is that of Cost (a.k.a. budget). Your customer and/or sponsor do not have infinitely deep pockets of cash to fund your project. Instead, they usually have a cost cap constraint. Further, they want to know up front (and with a level of confidence) how much the overall effort is going to cost. More importantly, they don’t want you to exceed this amount.

They might also not have all the money currently available, and can/will parcel it out the project on a fixed timescale. This is known as a funding profile, and it can be an added layer of constraint placed on a project.

The Golden Triangle Must Be Continually Balanced

This concept of a golden triangle of scope and the three constraints is vitally important for you as a PM to grasp. In a sense, these are the four things that have to be defined and documented at the outset of a project. They define the “ground rules” you must operate within. And, just as importantly, they must be constantly balanced and traded off with each other during the course of a project.

One way to think of the golden triangle is to imagine a linkage system. Scope is in the middle, and linkage bars connect to the three constraints of Quality, Time, and Cost. If the allowable cost is reduced, pressure is applied to one or more of the other three elements. E.g., either schedule must slip, quality must be lowered, and/or scope reduced. There is no free lunch in project management. One part of the triangle can never be changed without affecting at least one of the other three.

The four components of the Golden Triangle are intrinsically linked together. When you “push” on one, at least one of the others will have to “react.”

The four components of the Golden Triangle are intrinsically linked together. When you “push” on one, at least one of the others will have to “react.”

For example, let’s imagine that your customer comes to you halfway through the house project and says that he wants to increase its scope. Specifically, he says that he wants to increase the size of the detached garage from 2-cars to 3-cars. What are you going to do?

First and foremost, it’s important to communicate with that customer that he’s asking for a formal increase in scope, which, when it takes place during the course of a project, is referred to as “scope creep.”

Further, you must point out there will likely be both a cost increase and a schedule slip due to this scope increase. Your job as a project manager is to calculate how much those increases will be, what their impact and risks are, and then clearly communicate this information to the customer. Further, ou must get formal approval from before implementing this change.

You typically also need to identify and communicate possible ways of minimizing the impact of the scope increase. For instance, you might be able to absorb some or all of the additional cost by reducing the level of quality on some of the delivered scope. Changing from expensive Italian marble flooring, for instance, to less expensive wall-to-wall carpeting could potentially save enough to pay for the larger garage. That is to say, the increase in Scope can be offset by a decrease in Quality.

Another common problem you might encounter is a customer asking for a faster delivery than originally agreed upon. Instead of nine months to build the house, the customer might come to you halfway through the project and ask that it be delivered a month early.

In this situation, you first job as PM is analyze and communicate. You might be able to crash the schedule or fast-track parts of it to decrease the overall project duration, but these things might come at the expense of additional money and/or reduced quality. Or, you might need to reduce the overall scope; e.g., not build the garage as part of the initial project. Again, all four things (scope, quality, schedule, and budget) can often be balanced and traded off against each other in an effort to find the best overall solution, but this must be done in transparent collaboration with the customer or sponsor.

Golden Triangle trade-offs are very common. Further, they are really nothing more than a question of balance, of give-and-take. There is no free lunch in project management, and this much be fully communicated to your customer. When pressures arise, you must either ask for additional resources (time, money) or reduce something like scope elsewhere in the project, reduce the level of quality, or let the schedule slip.

Prioritizing Scope and/or Constraints

Most projects have an intrinsic priority of importance that can be assigned to the scope and the triple constraints, with one or two of these things often having higher importance than the others. In other words, when making trade-offs and balancing between the constraints, you might have flexibility in changing only one or two of the constraints, but not the others.

For example, if you were managing the construction of a new nuclear power plant, the constraint of quality would almost certainly be much more important—and hence, less changeable—than that of schedule; i.e., it’s more important that the nuclear reactor be built to high quality requirements (and not leak radiation during operations!) then it gets built on time. When the customer comes and asks for additional scope, quality would not be something that you would/could relax to offset the cost of the additional scope. Instead, you would likely propose slipping the schedule or asking for more money.

In contrast, if you were put in charge of organizing and hosting a major public event, along with the associated construction of major supporting infrastructure, such as the hosting of the Olympic Games, the constraint of schedule (i.e., opening on time) would likely be much more important than the final cost, or perhaps even quality of the construction.

One of your primary jobs at the outset of a project is to work with your customer, sponsor, and other key stakeholders to predetermine the priority order of the the golden triangle. Do not wait until an issue arises before making this determination. Pre-determine these priorities, and, if possible, include this information in the Project Charter.

The Bottom Line

Every project is different, but they all have scope and constraints. Further, the interactions between these four things are similar between projects, large and small. One of your responsibilities as a project manager is to define the four foundational components of the project (Scope + the triple constraints of Quality, Time, and Cost) at the start of the project, document them, and then do your best to hold them all fixed throughout the life of the project—but when pressure is applied to one or more aspects of triangle, keep in mind which of the four are more important than the others. And above all, clearly and fully communicate to your customer, sponsor, and other key stakeholders what trade-offs and changes need to take place.

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Mark WarnerComment