The body mass index is a number that represents the fat content in a human body based on the height and weight of any individual and is applicable to both men and women. A Belgian mathematician and statistician named Adolphe Quatelet developed the body mass index during the 1830s. Hence, it is sometimes called the Quatelet Index.

A simple formula that can be used to derive the Body Mass Index is to divide a person's weight in kilograms and divide it by their height in meters squared.

Underweight people usually have a BMI below 18.5, while a normal BMI is between 18.5 and 24.9, while overweight people have a BMI between 25 and 29.9, and the BMI of an obese person is over 30.

The Body Mass Index (BMI) is an indicator of fat content in an individual's body and can signify the risks of disease and death that the person faces. It would help immensely if one kept a close watch on this number, so as to be aware of any health risks they face.

There are some flaws with the BMI system. For example, it overestimates the body fat in athletes and body-builders due to their muscular build and might underestimate the body fat content in old persons or others who, for some reason, have lost body mass. Other risk factors associated with the calculated BMI could be hypertension, high cholesterol, and high sugar.

The BMI measures one's weight relative to their height, as stated above, while the waist circumference measures abdominal fat. Combining these with information about that particular individual's additional risk factors yields the risk for developing obesity-associated diseases.