BODY MASS INDEX (BMI) is a simple ratio of weight for height, often used to classify obesity and overweight. The index is calculated as the ratio of body weight in kilograms to the square of height in meters (kg / m2). BMI is the most convenient measure of the level of obesity and overweight in a population, since it is the same for both sexes and for all age groups of adults.
For example: your height is 1.7 m, your body weight is 78 kg. We square 1.7 m - we get 2.89 m2. After that we divide 78 kg. 2.89 m2. We get a figure of 26.9, which will be your BMI, indicating that you are overweight.