BMI

Body Mass Index (BMI) is a simple measure used to assess body weight relative to height. It is calculated by dividing a person’s weight in kilograms by the square of their height in meters (BMI = weight kg / [height m]^2). For those using pounds and inches, BMI can be calculated as (weight lb / [height in]^2) × 703.

In adults, BMI is commonly used to categorize weight status: underweight is defined as a BMI below 18.5, normal weight as 18.5 to 24.9, overweight as 25 to 29.9, and obesity as 30 or higher. These ranges are guidelines and can vary slightly by organization or population.

BMI serves as a screening tool in clinical and public health settings and is used in research to estimate disease risk related to body weight. It is not a direct measure of body fat or its distribution, and it does not distinguish between lean mass and fat. Consequently, individuals with high muscle mass may have a high BMI despite low body fat, while others with normal BMI may have excess body fat. BMI is also less reliable for older adults, the elderly, and people with certain conditions.

For children and adolescents, BMI is interpreted using age- and sex-specific percentiles rather than fixed cutoffs, reflecting growth patterns. In addition to BMI, other measurements such as waist circumference or body composition assessments may be used to provide a more complete picture of health risk.

Historically, BMI was developed in the 19th century by Adolphe Quetelet and later adopted for public health and clinical use, remaining a widely used, quick screening metric.