What is BMI

BMI, or body mass index, is a metric to compare your weight with the healthy weights for your height. BMI is calculated as your weight divided by the square of your height. A BMI score of 18.5 to 25 is considered healthy. Anything lower is considered underweight and anything higher is considered overweight. BMI is often used as a starting point to figure out how healthy you are.

History

The body mass index was invented by Adolphe Quetelet in the 1830s. Quetelet was a Belgian mathematician and physicist. BMI was originally called the "Quetelet Index." In the late 1900s, physicians started noticing a correlation between high body weight and early mortality. They searched for a measure of weight and decided that the Quetelet Index was the best option. In 1972, Ancel Keys published a paper that popularized the term "body mass index." Today, BMI is still widely used as an indicator of health.

Weight Categories

There are several different BMI charts that account for age, sex, and ethicity. The standard BMI chart by the World Health Organization (WHO) considers a healthy BMI to be between 18.5 and 25. Additional weight categories for the standard BMI chart can be found on our BMI chart page.

Age, Sex, and Ethnicity

The healthy BMI range varies by demographics. For example, women have tend to have a higher BMI than men. This is because women naturally have more body fat than men on average. A woman can have a slightly higher BMI and still be just as healthy. There is a similar discrepancy with ethicity. People in Eastern countries tend to have less body fat than people in Western countries. Therefore, Eastern BMI charts are adjusted so that the BMI categories have lower weights.

The BMI chart by WHO was designed for adults age 20 to 65. Children tend to have a lower BMI than adults, so WHO's BMI chart will not accurately assess their weight. Since children's BMI vary greatly with age, it's common to compare a child's BMI with the average BMI for their age. Here is a graph showing the average BMI for children.

Interpreting Your BMI

An unhealthy BMI can be an indicator of many health problems. A high BMI increases risk of:

  • Stroke
  • Heart disease
  • High blood pressure
  • Type 2 diabetes
  • Hypertension
  • Several types of cancer
  • Gallstones
  • Liver problems

For a more accurate assessment of your health, we recommend that you consult a licensed physician.

Limitations

Your BMI may not accurately reflect your actual state of health. Your weight and height are not enough to determine how healthy you are. For example, body builders have a very high BMI because of their muscle mass. On a BMI chart, they will be considered "overweight." However, body builders usually have a much lower body fat percentage than other people with the same BMI. Therefore, they are much more healthy than most people with the same BMI.

If you enter your age and sex in our BMI calculator, we will also calculate your body fat percentage. Your body fat percentage, combined with your BMI, gives you a more accurate assessment of your health.