BMI Calculator

About BMI Calculator

Body Mass Index (BMI) is a widely used screening measurement that compares a person's weight with their height. It is calculated by dividing body weight in kilograms by height in meters squared. BMI provides a standardized numerical value that can be used to classify weight status in adults and to identify ranges that may be associated with different health risks.

BMI is particularly useful because it provides a simple and inexpensive way to screen large populations and individuals for weight categories. However, BMI is not a direct measurement of body fat and does not determine a person's complete health status. It should therefore be interpreted together with other information such as waist circumference, body composition, blood pressure, metabolic measurements, physical activity, nutrition, and medical history.

How BMI Is Calculated

For metric measurements, BMI is calculated by dividing weight in kilograms by height in meters squared. Because height is often entered in centimeters, the calculator first converts centimeters to meters.

For example, a person who weighs 70 kg and is 175 cm tall has a height of 1.75 meters. Their BMI is calculated as 70 divided by 1.75 squared, producing a BMI of approximately 22.9 kg/m².

Adult BMI Categories

For adults, standard BMI categories are used to classify BMI values. A BMI below 18.5 is categorized as underweight, a BMI from 18.5 to below 25 is considered healthy weight, a BMI from 25 to below 30 is classified as overweight, and a BMI of 30 or higher falls within the obesity category.

Adult obesity can be further divided into three BMI classes. Class 1 obesity corresponds to a BMI of 30.0 to 34.9, Class 2 corresponds to 35.0 to 39.9, and Class 3 corresponds to a BMI of 40.0 or higher. Class 3 is sometimes described as severe obesity.

Estimated Healthy Weight Range

This calculator also estimates the body-weight range corresponding to the adult BMI range of 18.5 to 24.9 for the entered height. This is a mathematical reference range based on height and standard BMI boundaries.

The estimated range should not automatically be interpreted as an individual's ideal or medically recommended weight. People with the same height can have substantially different muscle mass, bone mass, body-fat levels, and body-fat distribution.

What BMI Can Tell You

BMI can be useful as an initial screening measurement because unusually low or high BMI values can be associated with increased risk of certain health conditions. In adults, higher BMI values, particularly within the obesity range, are associated at the population level with increased risk of conditions such as type 2 diabetes, cardiovascular disease, high blood pressure, and abnormal cholesterol levels.

A low BMI can also be clinically relevant. Being underweight may occur because of inadequate nutritional intake, underlying illness, changes in appetite, digestive problems, or other factors. BMI alone cannot determine why a person's weight is low or high.

Limitations of BMI

One of the most important limitations of BMI is that it does not distinguish between fat mass and lean mass. Muscle is denser than fat, so a person with substantial muscle mass can have a relatively high BMI without having an excessive amount of body fat.

BMI also does not show where fat is stored. Abdominal and visceral fat can be particularly relevant to metabolic health, which is why waist circumference and other measures can provide additional information that BMI alone cannot provide.

Age, sex, ethnicity, muscle mass, bone structure, pregnancy status, hydration, and other individual characteristics can also affect how meaningful a BMI value is for a particular person.

BMI for Children and Teenagers

The adult BMI categories used by this calculator should not be applied to children or teenagers. Because children and adolescents are still growing, their BMI must be interpreted in relation to age and sex using BMI-for-age percentiles rather than the fixed adult BMI categories.

For children and adolescents, a BMI below the 5th percentile is generally categorized as underweight, the 5th to below the 85th percentile as healthy weight, the 85th to below the 95th percentile as overweight, and the 95th percentile or higher as obesity.

BMI and Overall Health

BMI is only one part of a broader health assessment. A more complete evaluation may include waist circumference, blood pressure, blood glucose, cholesterol levels, physical activity, dietary patterns, sleep, family history, medical conditions, medications, and physical examination findings.

Two people with the same BMI may therefore have very different health profiles. BMI should be used as a screening tool rather than as a standalone diagnosis.

Understanding Your Result

The result section above shows your calculated BMI, the corresponding adult BMI category, the mathematical healthy-weight range for your height, and the formula used to obtain the result. When the BMI falls within the obesity range, the result also identifies the corresponding obesity class.

The healthy-weight range is calculated using BMI values from 18.5 through 24.9. This range is intended as a reference based on height and should not be treated as a personalized weight-loss or weight-gain target.

Example BMI Calculation

Important Considerations

BMI calculations are mathematical estimates and should be interpreted according to the appropriate age group. This calculator is designed primarily for adult screening and does not calculate BMI-for-age percentiles for children and adolescents.

A BMI result should not be used by itself to diagnose a disease or to determine whether a person is healthy or unhealthy. If you have concerns about your weight, body composition, nutrition, or health risks, a qualified healthcare professional can interpret BMI together with your individual medical history and other clinical measurements.