Difference Between ROM Estimate Vs Definitive Estimate

ROM estimates and definitive estimates differ from one another in terms of their degree of detail and related accuracy. A ROM estimate provides a high-level overview of the project. In contrast, a definitive estimate provides an accurate breakdown of the scope.

There's a lot of confusion out there about the difference between a ROM estimate and a definitive estimate. So, in this post, we'll explain the two terms, and offer some tips on how to choose the right one for your project. We'll also provide a few examples to illustrate the difference. Let's get started!

Difference Between the 2 Types of Estimation

A ROM estimate is a rough estimate of the cost of a project. It's not as detailed or specific as a definitive estimate, but it can be used to establish the scope of work and budget for projects still in development.

A definitive estimate gives an analysis of the resources needed to complete it, and a cost estimation with detailed explanations behind each line item budgeted for each task or activity that has been identified within the scope document.

ROM Estimate

Definitive Estimate

ROM estimate is a tool that is used to determine how much work a project will require.

A definitive estimate is a very specific number that project managers use to determine the amount of work that will be required to complete a given project.

It is a prediction of the total hours, days, and weeks that will be required to complete a project.

It is the most accurate estimate that can be made and ensures that the project is completed on time and within budget.

It is important to use ROM estimates when planning and estimating work in order to make accurate scheduling decisions.

A definitive estimate is based on current knowledge and past experience, as well as the current state of the project.

Scope Creep

Scope creep is a change in the scope of a project. It's different from change orders, which are documents that change the size of a project. It is a common problem that can occur when an organization expands its work beyond the original boundaries established in the project plan. This occurs when new tasks and objectives are added, without taking into account the changes that might have been made to other parts of the project or when existing resources are redirected to address new concerns.

This can lead to delays and increased costs, as well as decreased quality on various aspects of the project. The best way to avoid scope creep is to stay focused on task goals and timeline targets from start to finish and make sure all stakeholders understand how their contributions will impact overall success.

If you find yourself struggling with scope creep, it may help to take some time for reflection and analysis. This will help you identify where your efforts should be concentrated so that you can continue meeting your stated goals while minimizing risk and cost overruns.

How to Develop a ROM Estimate?

Developing a ROM estimate is a complex process that requires the use of advanced software. The most common type of software used to develop estimates is Cost Management Software (CMS). CMSs provide you with the ability to create estimates, run reports and manage your project from start to finish.

The process for developing an estimate includes the following −

  • Setting up your projects in terms of duration, cost, and schedule; can be done manually or through software that automatically does it for you.

  • Estimating labor costs based on job descriptions; can be done manually or through software that automatically does it for you.

  • Determine the scope of the project; What are the specific components that need to be completed?

How to Develop a Definitive Estimate?

A definitive estimate is a more accurate picture of the project cost. They are also used to confirm that an estimate is based on a realistic scope and work breakdown structure.

The method for developing a definitive estimate differs from that of creating an original ROM, in that it involves additional planning and review steps −

  • Analyze your current situation; What needs to be done? What resources do you need? How much will it cost?

  • The development team must be identified and assigned tasks based on their skills, experience level, etc., before starting any work on your project.

  • Once everyone has been assigned tasks or roles within their respective areas, you will want them all involved in determining how much time each task will take as well as how many resources need to be allocated toward completing these duties until the completion date at hand.

  • Create an idealized scenario or model of how your project will play out. This includes everything from expected results to possible obstacles and solutions.

  • Develop realistic estimates based on the information from your scenario analysis and your knowledge of current trends and practices in related fields. Be conservative with your estimates at first - you may find that they change as you get more information about the project.

Which One of The Estimates is Better?

The two types of estimates are differentiated by their degree of detail and related accuracy. A ROM estimate is a preliminary estimate that may change as you develop new information. A definitive estimate is an accurate final figure based on all the information available at the time it is made.

The benefits of using ROM or definitive estimates will depend on the specific situation. However, both methods have their own advantages and disadvantages.

The main advantage of ROM estimation is that it allows for more precision in project management. This is because each task can be assigned a fixed value, which reduces the risk of overestimating or underestimating tasks. Furthermore, by tracking actual progress against planned progress, you can quickly identify any issues early on in the project cycle.

On the other hand, definitive estimates are simpler and more accurate than ROM estimates and may be easier to communicate with stakeholders. They also tend to provide a better estimate of how long a task will take to complete.

Additionally, Definitive Estimates help prevent over-engineering projects - by providing a concise overview of an entire project's scope and budgeting for potential risks and contingencies upfront.


As you can see, there is a lot of difference between the two types of estimates. The main difference is that a ROM estimate has more details and less accuracy. However, this type of estimation is used by many companies to develop their projects and it can be more challenging to accomplish because it requires more time and effort to complete them properly.

On the other hand, we do not recommend using this method if you need precise numbers or high-quality work as it may end up costing your company excess funds due to scope creep. Both these estimates have pros and cons but they both can be quite helpful when used together. It all depends on your goals and the context in which you are estimating the job.

Updated on: 29-Dec-2022


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