Body Mass Index (BMI)

What is Body Mass Index (BMI)?

BMI is a mathematical calculation used to measure a person’s percentage of body fat. The formula for BMI is a person’s weight in pounds divided by the square of their height in inches. With the help of a calculator you can quickly get your BMI. Learn if you’re a candidate for bariatric surgery.



In general, BMI is an easy-to-perform method of screening for weight category, for example underweight, normal or healthy weight, overweight, and obesity.

Health Risks of Obesity

According to the Centers for Disease Control and Prevention (CDC), more than one-third of U.S. adults (34.9% or 78.6 million) are obese.

There are various medical conditions that are associated with obesity, such as:

  • Heart Disease
  • Diabetes
  • Hypertension
  • Osteoarthritis
  • Liver Disease
  • Sleep Apnea
  • Depression
  • Acid Reflux

BMI Ranges

A high BMI can be an indicator of high body fatness. BMI is commonly referenced in terms of bariatric surgery candidates. BMI is a good indicator of a person’s weight category and health.

  • Underweight: BMI less than 18
  • Normal: BMI 18-25
  • Overweight: BMI 25-30
  • Obese Class I (Moderately Obese): BMI 30-35
  • Obese Class II (Severely Obese): BMI 35-40
  • Obese Class III (Very severely obese): BMI over 40

How good is BMI as an indicator of body fatness?

The correlation between the BMI and body fatness is fairly strong but even if two people have the same BMI, their level of body fatness may differ.

In general,

  • At the same BMI, women tend to have more body fat than men.
  • At the same BMI, older people, on average, tend to have more body fat than younger adults.
  • At the same BMI, athletes have less body fat than do non-athletes.

The accuracy of BMI as an indicator of body fatness also appears to be higher in persons with higher levels of BMI and body fatness. While, a person with a very high BMI is very likely to have high body fat, a relatively high BMI can be the results of either high body fat or high lean body mass (muscle and bone). A trained healthcare provider should perform appropriate health assessments in order to evaluate an individual’s health status and risks.