BMI stands for Body Mass Index. It is a one size fits all formula that yields a number, which, supposedly indicates if an individual is underweight, overweight, or within a healthy range. It is based solely on height and weight. It makes no allowances for age, gender, body-frame size or body fat percentage. The only restriction for the BMI calculation is that it is only for adults who are at least four feet ten inches tall.
You can learn what your BMI is by consulting the BMI Chart. The chart is divided into 17 columns, one for each BMI of 19 through 35. It is also divided by rows corresponding to height in inches from 58 to 76. Each intersection of column and row is filled in with a weight in pounds. To find your specific BMI, go to the row that identifies your height, and move across that row, column by column, until you find your weight. The BMI heading of the column that holds the intersection of your height and weight is your BMI.
How to Use a BMI Chart
The BMI Chart, as just described, is based on a formula. First, you take your height in inches and square it. Then, you take your weight in pounds and divide it by your height squared. The final step it to take the previous result and multiply it by 703.
As an example, we’ll use an individual who weighs 152 pounds and is five feet and seven inches tall, or 67 inches. To square something is to multiply it by itself, so 67 squared is 67 times 67, or 4489. Then, by dividing the individuals weight in pounds, 152, by his or her height squared, or, as we calculated, 4489, yields, to three places, 0.0339. The final step is to multiply the last result by 703, which gets us a BMI of 23.83.
The next step is to consult a set of ratings, published by the National Institute of Health (NIH), by which we can evaluate our subject’s BMI. The NIH defines a BMI of less than 18.5 as underweight, a BMI of 18.5 to 24.9 as Healthy, BMI’s of 25 to 29.9 as overweight, and any BMI calculated as over 30 as obese.
Thus, our subject is within the high end of the range of the BMI accepted as healthy.
The problem with BMI is obvious. Our individual could be a college wrestler of age twenty with five percent body fat, a twenty-eight inch waist and a forty-two inch chest. Or the, individual could be an eighty year old man with a sunken chest and a thirty-five inch waist. BMI makes no allowance for anything else other than height and weight to access whether an individual is at the correct weight. Age, sex, and body fat composition are irrelevant to calculating the BMI, which belies common sense.