A Rough Order of Magnitude (ROM) Estimate is an initial estimate of the cost of a project or parts of a project, with a rough accuracy range. This estimate provides stakeholders and decision makers with a general idea of the project cost’s order of magnitude.
The ROM estimate is refined over time as more information becomes available during the project, following the concept of progressive elaboration.
Key Characteristics
- Early-Stage Estimate – Typically developed during initiation or conceptual planning
- Low Accuracy – May have a range of –25% to +75% depending on project context
- Supports Feasibility Decisions – Used to evaluate whether to pursue, fund, or prioritize efforts
- Subject to Revision – Becomes more precise as scope and requirements are clarified
Example Scenarios
- Estimating $2 million ±75% for a capital project based on a high-level scope
- Providing a cost range for proposal evaluation in portfolio selection
- Using historical data to forecast rough costs for a new initiative
Role in Cost and Scope Planning
- Enables Early Decision-Making – Provides directional insight before detailed planning
- Supports Progressive Elaboration – Refined into more accurate estimates over time
- Establishes Initial Baselines – Forms a starting point for cost evaluation and adjustment
- Informs Stakeholder Expectations – Communicates uncertainty while enabling planning
See also: Estimate at Completion (EAC), Definitive Estimate, Progressive Elaboration, Cost Management Plan, Project Charter.