What is BMI and why is it important?
BMI stands for Body Mass Index and it is a measure of body weight relative to height. The higher the BMI, the greater your body weight is relative to your height.
How is BMI calculated?
If you live in the USA, you need to know your height in inches and your body weight in pounds. Then you would apply the following formula to obtain your BMI value:
BMI = (Body weight in Pounds x 703) divided by (height in inches x height in inches).
So, for someone who weighs 102 pounds and is 5 feet tall, the calculation is
(102 x 703) divided by (60 x 60) = Approx. 20
If you live in a country where the standard measures are metric, then you need to know your height in meters (m) and your body weight in kilograms (kg), and fractions thereof. If you know your height in centimeters (cm) and your body weight in grams (g) then divide the centimeters by 100 to obtain meters, and divide the grams by 1,000 to obtain kilograms. Then apply the following formula:
BMI = (Body weight in kilograms) divided by (height in meters x height in meters)
Once you have obtained your BMI value, you would read off your body weight status from the following scale.
BMI and Weight Ratings
Below 18.5 = Underweight
18.5 – 24.9 = Normal Weight Range
25.0 – 29.9 = Overweight
Over 30.0 = Obese
Over 40.0 = Morbidly Obese
There are clear health risks associated with being overweight or obese and these will be described in detail in a following report.
Are there exceptions to the direct interpretation of this scale? Yes. I am aware of three exceptions. The first is babies who can be quite chubby for the first few months of their life but we would not be necessarily concerned about their health risks because of this. Babies and infants are not really considered with respect to BMI. The second is bodybuilders whose high BMI reading would be explained largely by their high muscle mass and not by excessive fat deposits. And the third is someone who has lost a limb because this would result in an underestimation of body weight relative to height. However, for the vast majority of the population, the Weight Ratings scale above would be applicable.
© Christopher J. Jones, M.Sc., Ph.D.
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