What is mass body index?

Body mass index (BMI) is a measure of body fat based on height and weight. It can be calculated manually (see related questions) or by using a BMI calculator such as the ones in the related links section from the CDC. They have calculators for both adults and children/teens and can be used with English or Metric measurements.

BMI is used by medical professionals, nutritionists, and others to roughly measure the extent of obesity (or an underweight status) in individuals. It should be used as a guideline since it is not 100% accurate (for example, muscle weighs more than fat and you can get skewed results if you are a body builder with muscle mass but not fat).