What is Rough Order of Magnitude (ROM) in Estimation

Rough order of magnitude estimation

Rough Order of Magnitude (ROM) estimation is a high-level estimation technique used in software development project management to provide a rough idea of the effort, cost, and duration of a project. It is typically done early in the project’s lifecycle when there is limited information available. ROM estimates are characterized by their wide range and lack of detail.

The purpose of ROM estimation is to quickly assess the feasibility and potential impact of a project. It helps stakeholders make informed decisions about whether to proceed with a project, allocate resources, and prioritise initiatives. ROM estimates are not meant to be highly accurate or precise but rather serve as a starting point for further planning and refinement.

ROM estimation is often based on expert judgment and historical data from similar projects. It involves making broad assumptions and extrapolating from past experiences. Since ROM estimates lack detailed requirements, they are subject to a higher degree of uncertainty and can vary significantly as more information becomes available.

The typical range of ROM estimates is usually expressed in terms of an order of magnitude, such as a factor of 10, 100, etc. The wider the range, the less precise the estimate.

It’s important to note that ROM estimates are not intended to replace more detailed estimation techniques used in later stages of project planning. As the project progresses and more information becomes available, the estimates should be refined using techniques like analogous estimation, parametric estimation, or bottom-up estimation to improve accuracy.


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About the Author: Anuj Seth

Anuj is a certified PMP with over 20 years of Software Development and Management experience. He founded PM Tips in 2020. Contributors are welcome. Drop him a note via the Contact page.

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