Body Mass Index

What is the body mass index?

The body mass index (BMI) is a calculated value which allows you to define how well the mass of the human body corresponds to the height and consequently a degree of over- or underweightness. BMI was developed by Belgian scientist Adolphe Quetelet in 1869. Using BMI you can try to estimate the risk of developing an illness due to excess or low weight. As of today, there are several variations of the body mass index (e.g. BMI Prime, Ponderal Index PI). In our BMI calculator we use classical BMI which is calculated with the following formula:

BMI formula

BMI usage

There are some threshold BMI values for different weight categories. When the BMI parameter is analyzed, individual weight and sex should be taken into account as well. Once you have calculated your BMI you can compare it with the threshold values in the table and determine what the group you belong to.
BMI value Group
less than 18.4 Underweight (for the given height you have low weight).
from 18.5 to 24.9 Normal balance between the weight and the height.
over 25 Overweight (for the given height you have excess weight).

BMI for children and teenagers

For children and teenagers BMI is calculated using the same formula as for adults, but the index is applied in a different way. Calculated BMI values are compared with the BMI values for children with the same age and sex. If the calculated index for a child is less than the index of 5% children in the same age group, then the child has low weight. If BMI is more than that of 95% children, the child is in the obese category. If their BMI are in range from 85 % to 95 % children are overweight.

BMI limitations

The body mass index just estimates the correlation between the weight and the height of a person and tells nothing about the distribution of fat and muscle mass in the body. In other words relying just on the BMI value we can't tell definitely whether the person is thin or fat because they can have the muscle mass which influences BMI instead of the fatty mass (we can't say that bodybuilders are fat, can we?). Therefore we should take into account a number of other parameters along with the BMI.

Other parameters

  • Waist-to-height ratio: if the coefficient is 0.5 or more this means that a person has too much abdominal fat.
  • Percentage of fat in a body is calculated using the formula developed by Hodgdon and Beckett. This parameter is calculated in different ways according to sex because men usually accumulate the fat in their abdomen (apple shape) but women in the abdomen and hips (pear shape).
  • Waist-to-hip ratio: it is assumed that a WHR of 0.7 for women says about good health and fertility. For men the optimal value of WHR is 0.9.

Did you know

  • BMI was developed by Belgian scientist Adolphe Quetelet in 1869.
  • If you always eat good, but don't gain weight, that means you consume more energy than you get from food.
  • The more pounds you want to lose the more you have to change your life.