BMI

The Body Mass Index (BMI) is a simple screening figure that relates a person's weight to their height, giving a single number meant to reflect roughly how much body tissue someone carries. Because it depends only on weight and height, it is quick and inexpensive to work out, which is why doctors and health services around the world reach for it first. The resulting value is used to sort adults into broad bands — underweight, normal weight, overweight, or obese — with the "normal" range usually running from about 18.5 to 25. Where you fall in those bands is loosely linked to health risks, since very low or very high values are associated with a greater chance of certain illnesses. Its big weakness is that it cannot tell muscle from fat, so a lean, muscular athlete and an out-of-shape person can share the same score. The bands also shift with age, sex, and population, and separate charts are needed for growing children. For all these reasons BMI works best as a first, rough indicator that should be read alongside other measurements rather than treated as the final word on a healthy weight.