Body Mass Index (BMI) is an indicator of body fatness based on height and weight. Research shows that BMI correlates with body fat, so it can be used to determine whether your body fat level is too low, too high, or just right.
Remember, BMI only correlates with body fat, but the relationship differs by age and gender. Only direct measures of body fat, such as underwater weighing, can provide a true measure of body fat. However, direct measures are expensive and time-consuming, whereas BMI is quick and easy.
BMI is a simple function of height and weight:
BMI = weight (kg) / [height (m)]2
Your BMI determines your weight category based on standards used by the Center for Disease Control and the World Health Organization.
| BMI | Weight Status |
|---|---|
| Below 18.5 | Underweight |
| 18.5 - 24.9 | Normal |
| 25.0 - 29.9 | Overweight |
| Above 29.9 | Obese |
Remember, BMI only correlates with body fat, but the relationship differs by age, gender, and body composition. For example,
According to BMI, Brad Pitt, Michael Jordan and George Clooney are "overweight". BMI is a quick tool, but not necessarily an accurate one, in assessing your overall health.
BMI is calculated the same way for all ages, but its interpretation differs for children and teens.
A child's weight category is determined by age and sex, as well as BMI.
For more information, see the CDC's BMI calculator for Children and Teens.
BMI was originally called Quetelet's index, after Lambert Adolphe Quetelet (1796 – 1874), a Belgian statistician who discovered that, for adults aged 20 and over, body mass increases as height squared increases.