It's good to keep in mind that your BMI is only an estimate. Do not make unnecessarily hasty generalization about thinness or obesity.
BMI is a measure of body weight based on a person's weight and height. It is defined as the body weight divided by the square of the body height.
After calculating your BMI you will also know how much you should either fatten or lose weight to reach the normal weight limits. This estimate is only for the 20 to 60-year-olds. BMI is used to estimate a healthy body weight, assuming an average body composition.
You can also calculate the new BMI developed by Nick Trefethen. This formula gives slightly different results. Values are smaller for taller people and bigger for shorter people.
The weight index calculation formula was originally developed by the Belgian mathematician, statistician, sociologist and astronomer Adolphe Quetelet (1796-1874). The name of the index at that time was "Quetelet Index", according to its inventor.
The formula developed by Quetelet can well be seen as part of his extensive life's work, where this genius saw mathematics and probability distributions in various phenomena around him. Quetelet studied the development of weight and height in men, women and at different ages and found that in adults the ratio of height to the square of weight remains very constant. Quetelet was not inspired by measuring fatness or thinness as such, but was interested in mathematics in nature and in people. Quetelet's work "A Treatise on Man and the Development of his Faculties" is a classic of sociology and statistics.
The index developed by Quetelet was positioned for its current purpose by the American Ancel Keys (1904-2004), whose specialty was the impact of nutrition on health. At this point, it had already been established that excessive adipose tissue had a detrimental effect on health. Keys reinvented the BMI. In the article "Indices of Relative Weight and Obesity", which appeared in the "International Journal of Epidemiology" in 1972, it is explained that it was Quetelet's formula that best estimated body fat percentage by using just height and weight. In the article, the formula is also renamed "body mass index". In addition to Ancel Keys, the authors of the article were Flaminio Finanza, Noburu Kimura, Henry Taylor and Martti Karvonen.
BMI is easy to calculate and the internet is full of different BMI calculators :). It also gives the average person a very accurate measure of the fat percentage.
However, it can be said that BMI is too generalizing. Women's fat percentage is somewhat higher than men's, but the same BMI and its interpretations are used for both men and women. So, in a way, BMI makes women slim and makes men fat because a greater proportion of men's weight is in muscle and less in fat. BMI also does not take into account individual differences such as muscularity at all.
BMI is also not suitable for assessing obesity or thinness in children and adolescents and older people.
The traditional weight index has been proposed to be changed. For example, Oxford University professor Nick Trefethen has suggested changing the exponent from 2 -> 2.5 and multiplying the result by 1.3. This so-called new BMI calculator can also be found on these pages. A feature of this calculator is that it is kinder to tall people. It gives 169 cm tall the same value as the traditional BMI, but gives a larger value for shorter people and a smaller value for taller people.
However, the new BMI suffers from the same problem as the traditional one. Although it may take account for the height better, it still does not account for individual differences in human body composition. And it is also not suitable for use by children, young people or the elderly.
Individual differences would be considerably better taken into account simply by measuring the waist circumference. Indeed, this is one of the best simple ways to indicate the amount of unhealthy body fat. In any case, BMI has maintained its position for an amazingly long time.
Quetelet: A Treatise on Man and the Development of his Faculties, 1835, In English 1842
Keys, Fidanda, Karvonen, Kimura, Taylor: Indices of relative weight and obesity, 1972, republished 2014
Trefethen: BMI (Body Mass Index), 2013
Enter food name and select from the list. Result is foods energy, protein, fat, carbohydrates, sugar, salt, etc. The data source is Fineli, the National Food Composition Database maintained by the Finnish National Board of Health and Welfare.