Rough Order of Magnitude (ROM) estimates are used to support high-level decision-making, long-range planning, or to provide quick, approximate answers to questions such as:
- “How big is the effort?”
- “At a high level, what kind of cost are we talking about?”
ROM estimates are especially useful early in a project when limited information is available and speed is more important than precision.
The first step is to determine whether a ROM estimate is appropriate. Review the project charter and scope documentation to understand the overall objectives and perform a preliminary complexity assessment.
Consider the following questions:
- Is the purpose of the estimate to support strategic decisions, long-range planning, or general sizing?
- Is a less precise estimate acceptable for the decision that needs to be made? For example:
- Can the organization afford an initiative within this general cost range?
- Will an estimate with an accuracy range of approximately ±50% be sufficient at this stage?
- Is there a need to produce the estimate quickly (e.g., within a few days to a week)?
If the answer to most of these questions is “yes,” a ROM estimate is likely appropriate.
ROM estimates are typically the first type of estimate developed during a project lifecycle and are often used during project initiation or early feasibility discussions. However, they should not be used when a high level of accuracy or confidence is required.
Important Note:
ROM estimating techniques are not suitable for detailed budgeting, contractual commitments, or final decision-making that depends on precise cost or schedule forecasts. As the project scope becomes clearer and more information becomes available, ROM estimates should be refined into more detailed and accurate estimates.