BMI Calculator

Calculator

How we calculate it

Body mass index is weight in kilograms divided by the square of height in meters. Imperial entries are converted to metric first, using 1 pound = 0.45359237 kg and 1 inch = 2.54 cm, so there is one calculation path regardless of the units you enter. The categories shown are the World Health Organization adult classification, which the CDC also applies to adults aged 20 and over: below 18.5 underweight, 18.5 to 24.9 healthy weight, 25.0 to 29.9 overweight, and 30.0 and above obesity, subdivided into class I, II and III at 35.0 and 40.0. The tool also shows the weight range that would put you at BMI 18.5 to 24.9 at your height, which is often more useful than the index itself. BMI was devised as a population screening measure, and that is the only thing it is validated for.

Important limitations

• BMI uses only height and weight, so it cannot distinguish muscle from fat. Muscular people are frequently placed in a higher category than their body composition warrants.
• BMI says nothing about where body fat is carried. Waist circumference and waist-to-height ratio add information about abdominal fat that BMI cannot capture.
• The WHO cut-points were derived largely from European-ancestry populations. The WHO has suggested additional action points at 23.0 and 27.5 for some Asian populations, and several countries apply their own adjusted ranges.
• These adult categories do not apply to children or adolescents, who are assessed against age- and sex-specific percentile charts.
• BMI is not validated during pregnancy or breastfeeding, for competitive athletes, for older adults with significant muscle loss, or for people with limb amputation or fluid retention.
• BMI is a screening measure for populations. It is not a diagnosis, a measure of health, or a measure of fitness for any individual.