What is BMI?
The Body Mass Index (BMI) is a measurement of a person's body composition based on their height and weight. It is widely used as a general indicator of whether a person has a healthy body weight for their stature. The value obtained from the calculation is used to categorize whether a person is underweight, normal weight, overweight, or obese depending on which range the value falls into. The World Health Organization (WHO) defines these ranges as: Underweight (below 18.5), Normal (18.5–24.9), Overweight (25–29.9), and Obese (30 and above).
BMI is calculated by dividing a person's weight in kilograms by the square of their height in meters. For example, someone who weighs 70 kg and is 1.75 m tall would have a BMI of 70 ÷ (1.75 × 1.75) = 22.9, which falls in the normal range. This simple formula makes BMI easy to compute and interpret, which is why it has become one of the most common screening tools used by healthcare providers and researchers worldwide to assess weight-related health risks.
While BMI is a useful screening tool, it has limitations. It does not distinguish between muscle mass and body fat, so athletes with high muscle composition may be classified as overweight even when they are in excellent health. Likewise, an older person with a "normal" BMI might still carry excess body fat. For a more complete picture of body composition, consider using our Body Fat Calculator, which uses measurements such as waist, neck, and hip circumference to estimate body fat percentage.