Editing Body mass index (section)

===BMI prime (exponent of 2, normalization factor)===
BMI Prime, a modification of the BMI system, is the ratio of actual BMI to upper limit optimal BMI (currently defined at 25&nbsp;kg/m<sup>2</sup>), i.e., the actual BMI expressed as a proportion of upper limit optimal. BMI Prime is a [[dimensionless number]] independent of units. Individuals with BMI Prime less than 0.74 are underweight; those with between 0.74 and 1.00 have optimal weight; and those at 1.00 or greater are overweight. BMI Prime is useful clinically because it shows by what ratio (e.g. 1.36) or percentage (e.g. 136%, or 36% above) a person deviates from the maximum optimal BMI.

For instance, a person with BMI 34&nbsp;kg/m<sup>2</sup> has a BMI Prime of 34/25 = 1.36, and is 36% over their upper mass limit. In South East Asian and South Chinese populations (see [[#International variations|§ international variations]]), BMI Prime should be calculated using an upper limit BMI of 23 in the denominator instead of 25. BMI Prime allows easy comparison between populations whose upper-limit optimal BMI values differ.<ref>{{cite journal | vauthors = Gadzik J | title = 'How much should I weigh?'--Quetelet's equation, upper weight limits, and BMI prime | journal = Connecticut Medicine | volume = 70 | issue = 2 | pages = 81–88 | date = February 2006 | pmid = 16768059 }}</ref>