Body mass index (BMI) A measure of body weight relative to height. BMI is a tool that is often used to determine if a person is at a healthy weight, overweight, or obese, and whether a person’s health is at risk due to his or her weight. To figure out BMI, use the following formula:
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A body mass index (BMI) of 18.5 to 24.9 is considered healthy. A person with a BMI of 25 to 29.9 is considered overweight, and a person with a BMI of 30 or more is considered obese.