order of magnitude estimate definition
Rough Order of Magnitude (ROM) Estimate. A rough order of magnitude (ROM) estimate is the least accurate estimate. The PMBOK Guide 4th Edition gives the guidlines that ROMs are -50% to +50% accurate, the PMBOK Guide 5th Edition gives the guidelines that ROMs are -25% to +75% accurate, or potentially even larger. rough order of magnitude (ROM) estimate is the least accurate estimate. The PMBOK Guide 4th Edition gives the guidlines that ROMs are -50% to +50% accurate, the PMBOK Guide 5th Edition gives the guidelines that ROMs are -25% to +75% accurate, or potentially even larger.