Library · Physiology
Body mass index
Make it clearer
Body mass index, usually shortened to BMI, is a simple piece of arithmetic: weight in kilograms divided by height in meters multiplied by itself. That is all it is.
That single number places an adult, in broad terms, into one of four boxes: underweight, normal weight, overweight, or obese. Its appeal is that it asks for nothing more than a scale and a tape measure, which is why it gets used so widely.
Its limitation comes from the same place. A scale has no idea what the weight is made of. BMI indicates the relative amount of body fat, but it does not calculate the percentage of body fat, and in someone with a lot of lean body mass, meaning a lot of muscle, it tends to overestimate that amount: a heavily muscled athlete can land in the overweight box without carrying excess fat. It is a signal worth a closer look, not a verdict.
In brief
Body mass index is calculated by dividing weight in kilograms by height in meters squared.
Using those two measurements from an adult, the method broadly places the person into underweight, normal weight, overweight, or obese categories.
It indicates the relative amount of body fat on a person's frame but does not directly calculate body fat percentage, and it tends to overestimate fat in people with a high lean body mass, such as athletes.
Sources (1)
- National Center for Biotechnology InformationBody Mass Index. StatPearls
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
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