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May 04, 2020
2 min read

What is a normal body mass index (BMI)?

A normal body mass index (BMI) is 18.5–24.9 kg/m2. BMI is a ratio of a person’s weight (in kilograms) to height (in meters squared).

Disclaimer

If you have any medical questions or concerns, please talk to your healthcare provider. The articles on Health Guide are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis, or treatment.

A normal body mass index (BMI) is 18.5–24.9 kg/m2

BMI is a ratio of a person’s weight (in kilograms) to height (in meters squared). A BMI of <18.5 kg/m2 is considered underweight, a BMI of 25.0–29.9 kg/m2 is considered overweight, a BMI of 30.0–34.9 kg/m2 is considered obese, and a BMI of >34.9 kg/m2 is considered extremely obese. BMI is often used as an indicator of how much excess body fat a person has. However, in individuals who are particularly muscular (such as bodybuilders), BMI may not be a good indicator of body fat.

Having a low BMI is associated with problems such as anemia, weakened immune system, electrolyte abnormalities, poor growth, and weight loss. Having a high BMI is a risk factor for many diseases, such as diabetes and heart disease. BMI can be brought back into the normal range by diet and exercise, including eating the recommended number of calories per day and getting the recommended amount of exercise per week. There are also medications and surgical procedures that can help individuals with a high BMI lose weight. You can read more about BMI here.

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What we mean by normal

In medicine, using the term “normal” can sometimes be off-putting. Saying something is “normal” implies that everything else is “abnormal.” Additionally, saying something is “normal” may not be accurate, since something that is “normal” for you may not be “normal” for somebody else. Therefore, instead of saying certain values are “normal,” alternative terminology may be to say that these values are “healthy” or “within the reference range.”

Additionally, some values have well-defined cutoffs, while others do not. For example, when looking at hemoglobin A1c levels, a value of 6.5 or greater is always diagnostic of diabetes. On the other hand, when looking at testosterone levels, some use cutoffs of 270–1,070 ng/dL while others use cutoffs of 300–1,000 ng/dL.

The information above represents values that are commonly used as cutoffs. However, depending on the specific source you’re looking at or the laboratory you go to, their values may be a little different.