BMI Calculator

Understanding Body Mass Index (BMI)

Body Mass Index, or BMI, is one of the most widely used screening tools for assessing weight status relative to height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, the formula divides a person's weight in kilograms by the square of their height in meters. The resulting number places you into one of four categories established by the World Health Organization: underweight (below 18.5), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 and above).

BMI is valued for its simplicity. It requires no special equipment, blood tests, or medical training. Doctors, insurers, and public-health researchers use it as a quick first step to identify people who may be at elevated risk for conditions such as type 2 diabetes, cardiovascular disease, and certain cancers. Population-level studies consistently show that BMIs well above or below the normal range correlate with higher mortality risk.

However, BMI has important limitations. Because it cannot distinguish between muscle, bone, and fat, athletes and highly muscular individuals often register as overweight despite having very low body fat. It also ignores where fat is stored. Visceral fat around the organs is far more dangerous than subcutaneous fat under the skin, yet BMI treats them the same. Age, sex, and ethnicity also influence the relationship between BMI and health risk. For these reasons, health professionals typically combine BMI with waist circumference, body fat percentage, blood markers, and lifestyle factors to form a more complete picture. Use this calculator as a starting point, not a diagnosis.