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What is BMI? 

BMI is a measure of a person's body size by calculating an individual’s height and weight, usually in kilograms and meters (BMI = kg/m2).

What does BMI measure? 

Body mass index (BMI) is a measure of your body’s height to weight ratio. Based on an individual's height, there is an ideal weight range that is considered healthy. BMI is an indirect measure of body fat, which strongly correlates with various metabolic and disease outcomes. 

How is BMI calculated? 

The first step in calculating body mass index (BMI) is collecting an updated height and weight measurement. If the measurements are taken using imperial measurements (pounds, inches) convert them to the metric measurements (kilograms, centimeters). For reference, 1lb= 0.45 kg and 1inch= 2.54 cm. The next part is a simple math equation: divide body weight in kilograms by height in meters squared. The same formula is used for both men and women. 

What is a good BMI?

A normal or healthy body mass index (BMI) is considered between 18.5-24.9. Having a healthy BMI reduces your risk of the development and progression of certain health conditions. When BMI is less than 18.5 or higher than 24.9, there is a greater risk of morbidity and mortality. A BMI between 25-29.9 is considered overweight and a BMI greater than or equal to 30 is considered obese. 

What are the limitations of BMI? 

For the majority of the population, a BMI of greater than 25 is considered overweight or obese. However, for individuals who are athletes or have increased muscle mass, a BMI greater than 25 is not considered unhealthy. This is because they are at a higher than normal weight due to increased muscularity vs. increased body fatness. Having more muscle mass is desirable when it comes to metabolic health. Therefore, a higher BMI due to increased muscle mass does not pose an increased health risk.

Learn more about Body Mass Index (BMI):

Photo of Kristin Ricklefs-Johnson

Medically reviewed by:

Kristin Ricklefs-Johnson, Ph.D., RD

Kristin is an RDN who also earned her Ph.D. in Nutrition from Arizona State University with an emphasis on insulin resistance, lipid metabolism disorders, and obesity. She completed her post-doctoral fellowship at Mayo Clinic where she focused on nutrition-related proteomic and metabolic research. Her interests include understanding the exact mechanism of action of various genetic variations underlying individual predispositions to nutrition-related health outcomes. Her goal is to help all individuals prevent chronic diseases and achieve long, healthy lives through eating well.

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