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How to Calculate Your Body Mass Index (BMI)

Medically reviewed on Sep 26, 2016 by L. Anderson, PharmD.

The terms “overweight” and “obese” have specific definitions in healthcare. Overweight and obese are both terms for a range of weight that is greater than what is considered healthy for a given height.Calculating you body mass index (BMI) can provide even more information about your health risks.

What is BMI?

For adults, overweight and obesity ranges are determined by using weight and height to calculate a number called the body mass index (BMI). BMI is used because, for most people, it correlates with their amount of body fat. BMI is an indirect measure of body fat, but is more convenient than some direct measures of body fat, such as underwater weighing, or dual energy x-ray absorptiometry.2 BMI is also important because the use of many weight loss drugs are based on a whether a person has reached a certain BMI.

Other factors are used in addition to BMI to determine if someone is at risk for weight-related diseases. In addition to BMI, an individual's

  • waist circumference
  • disease or lifestyle attributes, such as high blood pressure or lack of exercise

are predictors of obesity-related diseases, such as high blood pressure, high cholesterol, and type 2 diabetes. The National Heart, Lung, and Blood Institute guidelines recommend that these additional two predictors should be used in addition to BMI to assess weight-related health risk.3

People with increased muscularity may have a high BMI not necessarily due to excessive body fat, and these BMIs would typically fall in overweight range. However, muscle builders with BMIs in the obese range will usually have a large percentage of body fat.4

To calculate a BMI:

  • Multiply weight in pounds by 703.
  • Divide that answer by height in inches
  • Divide that answer by height in inches again

The CDC also has a BMI calculator you can use.

BMI Risk Categories

BMI Category
Under 18.5 Underweight
Between 18.5 – 24.9 Healthy
Between 25.0 – 29.9 Overweight
Between 30.0 – 39.9 Obese
Over 40 Morbidly obese

For more information about interpretation of BMI for overweight or obese children and teens, visit Childhood Obesity: A U.S. Epidemic

See Also


  1. Centers for Disease Control and Prevention (CDC). Overweight and Obesity. Accessed Sept. 26, 2015.
  2. Centers for Disease Control and Prevention (CDC). Assessing Your Weight: About Adult BMI. Accessed Sept. 5, 2016.
  3. Department of Health and Human Services. NIH. National Heart, Lung and Blood Institute. Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults. Accessed Sept. 5, 2016.
  4. Obesity. Accessed Sept. 26, 2015.