What is the body mass index?

Each time I do a Body Test on Wii Fit my body mass index (BMI) is computed and displayed for by viewing (dis)pleasure. Mine hovers in the 36-37 range, which is off-the-scale obese.

My ideal BMI according to Wii Fit is 22, which would put me at a sleek 140 pounds.

But how the heck is this calculated? The original BMI was developed in the mid-19th century by Adolphe Quetelet and is simply the ratio of a person’s mass to the square of his height. So if I express my mass in kilograms and my height in meters, then

BMI = mass in kg / (height in m)2

Or, if I don’t want to convert to the units that the rest of the world uses, I can just use pounds and inches, and multiply by 703:

BMI = 703 (weight in lbs) / (height in inches)2

(To see why 703 works, substitute 2.2026 lbs for 1 kg and 39.37 inches for 1 m. Now, 2.2026 / (39.37)2 is 0.001421, or 1/703.7.)

BMI is most useful on populations (i.e. large-number statistics) and there may be other reasons why a healthy person could have a high BMI. (I don’t think this applies to me. I’m just fat.) But clinically obese people like myself do run a higher risk of heart disease, diabetes, cancer, and other problems.

BMI is a measure that does carry some weight (!) but it’s possible that a BMI higher than 22 is just fine for some people. But again, it probably has to be quite a bit less than 37. 😉 )

1 thought on “What is the body mass index?”

  1. Just calculated mine, and I’m solidly in the “overweight” category. When I started working out over a year ago I was in the obese category. Funny how you never “feel” like your obese..

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