The Body Mass Index (BMI) is a measurement used to assess body weight. It describes the relationship between a person’s weight and height and is calculated using the following formula: BMI = weight (kg) / height (m)2. For example, if you are 1.70 m tall and weigh 60 kg, you would calculate your BMI like this: 60 / (1.70 x 1.70) = 20.76. So this would mean that you have a BMI of around 21. People who have a BMI between 18.5 and 24.9 are considered to have a normal weight. A BMI below 18.5 is considered to be underweight, and a BMI between 25 and 29.9 is considered to be overweight. People who have a BMI over 30 are considered to be obese. The BMI only says something about people’s total body weight, though, and nothing about their body fat. Two people could have the same BMI but a different amount of fat in their bodies. So a bodybuilder who has a lot of muscle tissue and little fat could have the same BMI as a person who has little muscle tissue and a lot of fat. Still, a BMI over 30 is usually a sign of a high percentage of body fat.