ROM (rough order of magnitude): definition and example
An early, rough estimate of cost, given before the design is developed enough to price properly.
By Jack Butler-Kettle · Updated
Guidance for England and Wales. Check the contract, amendments and facts that apply to your job.
What it means in practice
Read this alongside NRM 2: Detailed measurement for building works.
A rough order of magnitude is an early estimate based on limited information. It should state assumptions, exclusions, uncertainty and the purpose for which it can be used. It is different from an agreed quotation or a supported claim calculation, even when all three are expressed in pounds.
Keep estimates clearly labelled as information develops. Unpaid variation prevention helps distinguish early indications from instructed and agreed changes.
Worked example
The facts
A specialist gives an initial £8,000 to £12,000 estimate before the revised design is issued.
What happens
It records the assumed scope and explains why the figure is a range.
After receiving the design, it prepares a separate detailed quotation.
What this shows
The earlier estimate provides planning context without being represented as the final agreed price.