What is ROM Estimate

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Nov 04, 2022

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Estimation is a critical component of project management. Before a project begins, stakeholders want to know the budget because all initiatives need one. Therefore, project estimation needs to be done before the project is launched. This leads us to a kind of rough estimate known as Rough Order of Magnitude (ROM), which is provided to the stakeholders before they decide whether or not to move forward with the project.

The Need for ROM

Before understanding what ROM estimate is, it is important to understand its need and what brought it into existence.

Having the ability to estimate a project's cost is essential for success in the field of project management. Project managers who are having a tough time coming up with reliable and precise estimates can benefit a lot from this. Moreover, it helps to gain a thorough understanding of ROM and Definitive, which are two of the most crucial estimate metrics. In fact, project managers can apply these two metrics to their projects immediately.

A project manager may aid in the preparation of more precise estimates; first and foremost, it is crucial to ensure that all of the inputs used to calculate the cost are accurate. When estimating a project's cost, some project managers use historical data; while this might be effective in some circumstances, it will ultimately result in bigger differences between estimated and actual costs.

There are essentially two methods for estimating a project's cost. The ROM estimate, or rough order of magnitude estimate, is one of the most widely used methods. Using a firm estimate is an additional method of estimating project costs.

Any project management professional should be familiar with how both of these cost estimations operate because the expenses are calculated in them in distinct ways. Certainly, obtaining professional PMP Certification or PMP training can help in gaining competency in developing ROM estimates. A business may be more or less tolerant of deviation from the estimate depending on the methodology used.

What is ROM Estimate?

A ROM estimate is typically finished at one of the project's initial phases. A firm or business typically requests an approximate estimate rather than an exact cost when they need a ROM cost to be done.

A ROM estimate can easily have a plus or minus 50% difference between expected and real costs. It is important for anyone creating a ROM estimate to note that the estimate's accuracy can vary significantly, especially if the project is still in its early phases.

ROM Estimate: How to Prepare It?

A project management expert must finish the task to ensure the estimate is as accurate as feasible, even though ROM estimates have a more widely recognised range. Regarding price variation, there are bounds to what is allowed.

The completion of projects frequently takes several years. The cost of labour or raw materials over several years might be challenging to predict and plot. However, some inputs are well-known that the project manager will undoubtedly get right. In general, there is a greater potential for price variance the longer the project's time horizon.

The degree of fluctuation would not be acceptable, for instance, if a new house was predicted to cost $200,000 to build but ended up costing $1,000,000 instead. The known factors must be accurately estimated when creating cost estimates using this method.

Remember that the purpose of ROM calculations is to produce a rough estimate that is mainly accurate, even if it doesn't always fit into your plans. To attain a more acceptable result, you can find it tempting to use figures that are on the conservative side.

Unfortunately, utilizing false statistics completely undermines the purpose for which the estimation was originally developed. Excellent research can provide light on parts of your rough order of magnitude estimate where bias might be tempted to enter the picture.

All things considered, the variation of a ROM estimate is not great enough to dissuade you from making one. Similar to how a budget estimate is likewise utilized to establish your basis, a ROM estimate serves as a beginning point for moving forward. Managers should give budgets as a range, for instance, rather than merely single-point predictions.

Tools for Calculation of ROM Estimates

To assist project managers with providing likely ROM estimates, a number of useful tools are available. Project managers can get assistance from a variety of compatible suites of tools at various stages of the project. Software solutions that assist with ROM and Definitive Estimates are also among these. Additionally, ROM templates are available to help map out all the factors to consider.

Techniques for Calculation of ROM Estimates

When trying to understand what is ROM estimate, it is important to learn the techniques that can be used to calculate ROM estimates.

Analogous Estimation

This approach bases its estimation of the new project on information and experience from earlier or comparable initiatives.

Parametric Estimation

The parametric method uses a unit rate derived from prior projects to estimate the new project.

Three-point Estimation

The three-point method determines the most accurate value for a project by using optimistic, realistic, and pessimistic estimates. The three-point method's capacity to adjust for project timing uncertainty is its strongest feature.

T-shirt size estimation

The rough order of magnitude estimates provided by the T-shirt size method are expressed relative to one another rather than numerically.

A proper PMP certification or PMP training course is best to understand the tools and techniques used for the calculation of rough order of magnitude estimates.


The chances of the ROM estimates performing effectively throughout the project increase with their accuracy. It will, in fact, reflect what occurs throughout the full project life cycle. Only by fine-tuning as they go and taking into account new information can project managers increase their accuracy. StarAgile’s PMP certification and PMP training courses are designed and structured in a way to help project managers learn the techniques and tactics useful for calculating ROM estimates. Enrol now!


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