BMI Calculator (Body Mass Index)

Body mass index, or BMI, is a screening ratio that relates weight to height. The metric equation divides weight in kilograms by height in meters squared. Because the calculation needs only two common measurements, it is widely used in public health, routine adult screening, and research. This calculator also reverses the equation to show the weights corresponding to the standard healthy BMI boundaries for the entered height. Common adult categories classify BMI below 18.5 as underweight, 18.5 through 24.9 as healthy weight, 25.0 through 29.9 as overweight, and 30.0 or higher as the obesity range. These boundaries describe statistical groups, not a complete diagnosis for an individual. Risk can vary among people at the same BMI, and some clinical guidelines use additional context or population-specific thresholds. BMI cannot distinguish fat from muscle, bone, or water. A muscular athlete may have a high BMI without excess body fat, while an older adult can have a value in the healthy category despite reduced muscle and relatively high body fat. It also cannot show where fat is stored. Waist circumference, growth history, blood pressure, laboratory values, fitness, nutrition, sleep, medicines, pregnancy status, ethnicity, and family history may all add important information. For a consistent result, weigh with a reliable scale and measure standing height without shoes. Enter kilograms and centimeters, not pounds or inches. Day-to-day weight can shift with hydration, meals, clothing, and time of day, so trends measured under similar conditions are generally more informative than small changes in one reading. The displayed healthy weight interval is a mathematical reference and should not be treated as a required personal target. Standard adult BMI categories are not appropriate for children and teenagers, whose results are interpreted using age- and sex-specific growth charts. Pregnancy and some medical conditions also require different assessment. Anyone concerned about unexplained weight change, nutrition, body composition, or cardiometabolic risk should discuss the result with a qualified healthcare professional. A clinician can combine BMI with examination and relevant measurements to develop advice suited to the individual rather than relying on this screening number alone.