Body Mass Index (BMI) is a measure of body fat based on height and weight.

How to calculate Body Mass Index

Body Mass Index is a simple calculation using a person’s height and weight. The formula is BMI = kg/m2 where kg is a person’s weight in kilograms and m2 is their height in meters squared.

A BMI of 25.0 or more is overweight, while the healthy range is 18.5 to 24.9. BMI applies to most adults 18-65 years.

Why isn’t BMI used for muscle builders, long-distance athletes, pregnant women, the elderly or young children?

BMI is not used for muscle builders, long-distance athletes, pregnant women, the elderly or young children. This is because BMI does not take into account whether the weight is carried as muscle or fat, just the number. Those with a higher muscle mass, such as athletes, may have a high BMI but not be at greater health risk. Those with a lower muscle mass, such as children who have not completed their growth or the elderly who may be losing some muscle mass may have a lower BMI. During pregnancy and lactation, a woman’s body composition changes, so using BMI is not appropriate.


BMI is a measurement of a person’s leanness or corpulence based on their height and weight, and is intended to quantify tissue mass. Although BMI has limitations in that it is an estimate that cannot take body composition into account, it can be used as a general indicator of a healthy body weight based on a person’s height. The value obtained from the calculation of BMI is widely used to categorize whether a person is underweight, normal weight, overweight, or obese depending on what range the value falls between. These ranges of BMI vary based on factors such as region and age and are sometimes further divided into subcategories such as severely underweight or very severely obese. As previously mentioned, however, due to a wide variety of body types as well as the distribution of muscle, bone mass, and fat, BMI should be considered along with other measurements rather than being used as the sole method for determining a person’s “healthy” body weight.

Ponderal Index

The Ponderal Index (PI) is similar to BMI in that it measures the leanness or corpulence of a person based on their height and weight. The main difference between the PI and BMI is the cubing rather than squaring of the height in the formula (provided below). While BMI can be a useful tool when considering large populations, it is not reliable for determining leanness or corpulence in individuals. Although the PI suffers from similar considerations, the PI is more reliable for use with very tall or short individuals, while BMI tends to record uncharacteristically high or low body fat levels for those on the extreme ends of the height and weight spectrum.

BMI Table for Adults

This is the World Health Organization’s (WHO) recommended body weight based on BMI values for adults. It is used for both men and women, age 18 or older.

CategoryBMI range – kg/m2
Severe Thinness< 16
Moderate Thinness16 – 17
Mild Thinness17 – 18.5
Normal18.5 – 25
Overweight25 – 30
Obese Class I30 – 35
Obese Class II35 – 40
Obese Class III> 40


BMI Chart for Adults

This is a graph of BMI categories based on the World Health Organization data. The dashed lines represent subdivisions within a major categorization.

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BMI Table for Children and Teens, Age 2-20

The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and teens between age 2 and 20.

CategoryPercentile Range
Healthy weight5% – 85%
At risk of overweight85% – 95%