What Is a Rough Order of Magnitude (ROM)? June 27, 2025, 07:34:11 PM A rough order of magnitude is a quick guess of how much something will cost or how long it will take. People use it in construction to plan budgets or time. It’s not exact but gives a good idea. For example, if building a house costs around $100,000, that number might be a rough order of magnitude to help plan things early on. Quote Selected