ROM
Rough Order of Magnitude
Acronyms & AbbreviationsDefinition
A Rough Order of Magnitude (ROM) is a preliminary cost estimate used in government contracting to approximate the expected cost of a project or requirement before detailed specifications are available. ROMs are typically accurate within -25% to +75% of the final cost.
The government uses ROMs early in the acquisition planning process to determine budget feasibility, set aside funding, and decide whether to proceed with a formal solicitation. Contractors are often asked to provide ROM estimates during market research, RFI responses, or industry day events.
ROM accuracy levels (per AACE International):
- ROM / Class 5 — -25% to +75%. Based on minimal information. Used for screening and feasibility.
- Budget / Class 3 — -10% to +25%. Based on preliminary design. Used for budget authorization.
- Definitive / Class 1 — -5% to +10%. Based on detailed design. Used for bid/tender.
Tips for providing ROMs:
- Always label your estimate as a ROM and state the assumptions behind it
- Include a range, not a single number — this protects both you and the government
- ROMs are not binding commitments — but unrealistically low ROMs can set expectations you'll struggle to meet later
- The government may use your ROM to develop the Independent Government Cost Estimate (IGCE)
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