BMI Calculator

BMI, or body mass index, is a screening tool that takes into account a person’s height and weight. It slots people into four general weight classes: underweight, normal weight (or healthy weight), overweight and obesity.

BMI does not directly measure a person’s health, but it is used — along with other measures, including your physical activity, blood pressure and cholesterol levels — to assess your overall risk of developing certain diseases.

The normal weight category, also known as the healthy weight category, is defined as a BMI of 18.5 to 24.9 kilograms per square meter (kg/m²). A weight in this category is linked to fewer health problems than the underweight, overweight and obesity categories.

While this is considered the ideal category, keep in mind that BMI is not a perfect measure. For example, it does not take into account fat distribution, ethnicity and other factors that can affect your metabolic health.

Body mass index is a person’s weight in kilograms divided by the square of height in meters.

That depends. BMI can’t tell how much of your weight is from fat or muscle, so it misses important information for assessing your health risks. For instance, athletes can have a high BMI because of their muscle mass, even if they’re not overweight. Also, the definitions for the weight categories are based primarily on white populations, so the measurement may be less accurate for people of other races and ethnicities.

BMI doesn’t differentiate between fat, bone and muscle; therefore, it may be less accurate for older people, who tend to lose muscle mass and bone density as they age. (That’s why people over 65 may benefit from a slightly higher BMI, between 25 and 27.)

Research shows that the BMI definition of obesity overestimates risk in Black people and underestimates it in individuals of Asian descent, which may lead to inappropriate treatment and health disparities.