The body mass index (BMI), or Quetelet index, is a step for body shape based upon a person’s mass and height.
Devised in between 1830 and 1850 by the Belgian polymath Adolphe Quetelet during the course of developing “social physics”,  it is defined as the person’s body mass divided by the square of their height – with the value universally being offered in systems of kg/m2.
The aspect for UK/US systems is more specifically 703.06957964, but that level of accuracy is not significant for this calculation.
BMI can likewise be identified utilizing a table  or from a chart which shows BMI as a function of mass and height utilizing shape lines, or colors for various BMI categories. Such charts can easily allow 2 various sets of units of measurement to be utilized, which is frequently useful. 
The BMI is used in a wide range of contexts as a simple approach to examine just how much a person’s body weight departs from what is typical or desirable for a person of his or her height.
There is however often energetic dispute, especially relating to at which worth of the BMI scale the limit for obese and overweight need to be set, however likewise about a variety of perceived limitations and issues with the BMI.
Despite a wide variety of other, differently computed, ratios having actually been proposed,  none have actually yet been as widely embraced.
While the formula formerly called the Quetelet Index for BMI dates to the 19th century, the new term “body mass index” for the ratio and its appeal date to a paper published in the July edition of 1972 in the Journal of Chronic Illness by Ancel Keys, which found the BMI to be the best proxy for body fat portion among ratios of weight and height;   the interest in measuring body fat being because of weight problems ending up being a discernible concern in prosperous Western societies.
BMI was clearly cited by Keys as being proper for population research studies, and unsuitable for specific medical diagnosis. Nonetheless, due to its simplicity, it happened widely utilized for private diagnosis.
‘BMI’ provides a simple numeric measure of a person’s thickness or thinness, allowing health professionals to discuss overweight and underweight problems more objectively with their patients. However, BMI has become controversial because many people, including physicians, have come to rely on its apparent numerical authority for medical diagnosis, but that was never the BMI’s purpose; it is meant to be used as a simple means of classifying sedentary (physically inactive) individuals, or rather, populations, with an average body composition. For these individuals, the current value settings are as follows: a BMI of 18.5 to 25 may indicate optimal weight, a BMI lower than 18.5 suggests the person is underweight, a number above 25 may indicate the person is overweight, a number above 30 suggests the person is obese.
For a given height, BMI is proportional to mass. However, for a given mass, BMI is inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high compared to their actual body fat levels. In comparison, the Ponderal index is based on this natural scaling of mass with the third power of the height. However, many taller people are not just “scaled up” short people, but tend to have narrower frames in proportion to their height. Nick Korevaar (a mathematics lecturer from the University of Utah) suggests that instead of squaring the body height (an exponent of 2, as the BMI does) or cubing the body height (an exponent of 3, as the Ponderal index does), it would be more appropriate to use an exponent of between 2.3 and 2.7 (as originally noted by Quetelet). (For a theoretical basis for such values see MacKay.)