Why BMI is a bad measure of obesity (and what is better)

BMI, or body mass index, is calculated by dividing by weight by height squared. Specifically, it’s weight in kilograms divided by height in meters, squared. If you prefer pounds and inches, then it’s weight in pounds *703 divided by height in inches, squared. For example, if you are 5'8" tall and weigh 179 pounds. 179*703 = 125837. 5'8" is 68 inches, and 68² = 4624, finally, 125837/4624 = 27.21 and that’s your BMI. If you don’t like doing all that calculating, there are lots of online BMI calculators. According to the US Department of Health and Human Services, that BMI puts you in the category “overweight”. Their categories are:

• Underweight Below 18.5
• Normal 18.5 to 24.9
• Overweight 25–29.9
• Obese 30 and higher

For some people, these BMI categories make sense. For others, they are ludicrous. To rely on these numbers to tell if you are overweight is silly — they can be totally misleading, for several reasons:

Arbitrary BMI categories

The categories are arbitrary. If your BMI is 24.9 then you are “normal” and if it is 25.1 you are “overweight”. Is this sensible? That means that if you weighed 168 you would be “normal” and if you weighed 170, BOOM your BMI is over 25 and you are “overweight”.

BMI ignores everything but height

Not all people who are the same height are the same dimensions, even at their ideal weight…