Calculate your Body Mass Index instantly
Body Mass Index (BMI) is a simple measure using your height and weight to work out if your weight is healthy. The BMI formula divides an adult's weight in kilograms by their height in metres squared. A BMI of 18.5 to 24.9 is considered a healthy weight range. BMI is used worldwide by doctors and health organizations as a screening tool.
Metric: BMI = weight (kg) / height (m)²
Imperial: BMI = 703 × weight (lbs) / height (in)²
Calculate your Body Mass Index (BMI) instantly with our free calculator. BMI is a widely used screening tool that estimates body fat based on your height and weight. Get your BMI category, healthy weight range, and personalized health recommendations.
Body Mass Index (BMI) is a numerical value calculated from your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, BMI provides a simple way to categorize individuals as underweight, normal weight, overweight, or obese. The formula is: BMI = weight (kg) / height squared (m squared).
The World Health Organization (WHO) defines BMI categories as: Underweight (below 18.5), Normal weight (18.5 to 24.9), Overweight (25.0 to 29.9), Obesity Class I (30.0 to 34.9), Obesity Class II (35.0 to 39.9), and Obesity Class III (40.0 and above). These ranges apply to adults aged 20 and older.
While BMI is a useful screening tool, it has important limitations. It does not distinguish between muscle and fat mass, so athletes may have a high BMI despite being very fit. It also does not account for age, sex, ethnicity, or body composition. For a more complete health assessment, consider combining BMI with waist circumference, body fat percentage, and other health markers.
BMI thresholds may vary for different ethnic groups. For Asian populations, the WHO suggests lower cutoff points: overweight at 23+ and obese at 27.5+, as health risks increase at lower BMI values in these populations. Children and teens use age-and-sex-specific BMI percentiles rather than the adult categories.
A healthy BMI is between 18.5 and 24.9 for adults. This range is associated with the lowest risk of weight-related health problems. However, BMI is just one indicator of health and should be considered alongside other factors.
BMI may overestimate body fat in athletes and muscular individuals because it does not distinguish between muscle and fat mass. A bodybuilder could have an obese BMI while having very low body fat. Body fat percentage measurements are more accurate for athletes.
BMI is calculated by dividing your weight in kilograms by your height in meters squared: BMI = kg/m squared. In imperial units: BMI = (weight in pounds times 703) / (height in inches) squared.
For adults 20+, the same BMI categories apply regardless of age. For children and teens (2-19), BMI is interpreted using age-and-sex-specific percentiles because body composition changes during growth. A pediatrician can help interpret children's BMI.
A BMI of 25 or higher is associated with increased risk of type 2 diabetes, heart disease, high blood pressure, certain cancers, sleep apnea, and joint problems. The higher the BMI above normal range, the greater the risk.