In detail

Body Mass Index (BMI)


Definition: body mass index

Of the Body mass index (Abkьrzung: BMI) is a statistical index indicating the ratio of body weight to body size. Translated, the term means "body mass index". The body mass index is used to statistically estimate the body weight. The weight alone does not tell you whether a person is underweight, normal or overweight. For example, a 90kg man may be of normal weight (body size 2m) or overweight (body height 1.70m). With the BMI both details (body size and body weight) are taken together and expressed in a general index number.

BMI formula:

BMI = body weight / body sizeІ
Factors such as gender, body fat percentage or body structure are not taken into account in the formula. That's also the biggest weakness of the body mass index. Individual differences can not be taken into account, which is why the body mass index uses only as a rough guide.
Example calculations: Three persons, all weighing 74 kg. Subject 1 is 1.60m, subject 2 is 1.80m and subject 3 is 2.00m tall.
Test person 1: 74 kg / (1.60mІ) = 74 / 2.56 = 28.90 (BMI)
Test person 2: 74 kg / (1.80mІ) = 74 / 3.24 = 22.83 (BMI)
Test person 3: 74 kg / (2.00mІ) = 74 / 4.00 = 18.50 (BMI)
These calculations make it clear that the weight alone can not be an indication of the general nutritional status. Only the inclusion of the body size makes an approximate statement possible. The calculated index values ​​are then to be compared with the values ​​from the table.

BMI table:

Index values ​​from the WHO (World Health Organization) for adults:

TдtigkeitBMI value
underweightunder 18.5
normal weight18.5 to 24.99
Ьbergewicht25 to 29.99
obesityover 30,0