Body mass index (BMI) is a simple formula used as a preliminary determinant of whether you may be underweight or obese. Because it is a simple equation ignoring numerous factors, such as body frame and body fat percentage, BMI is not effective as a standalone diagnostic tool. Many athletes, for example, are defined as obese according to BMI because of their muscle mass, even though many are in excellent physical condition. But BMI is a good starting point to evaluating your overall health.
Step 1
Determine your height and weight. The height should be converted into inches, and your weight should be in pounds, although there are metric calculators online you could use if desired.
Step 2
Multiply your weight by 703. This only works if you calculate using pounds.
Step 3
Divide the number produced in the previous step by your height in inches squared. The full equation for BMI is:
BMI = W * 703 / H^2
W equals your weight in pounds, and H represents your height in inches.
Step 4
Use the BMI scale to determine where your BMI sits. A BMI below 15 indicates you are extremely underweight. Values between 15 and 18 indicate mildly underweight. The normal range is between 18 and 24. Numbers 25 to 30 are overweight, over 30 is obese, and anything over 40 is classified as morbidly obese.
Tips and Warnings
- If you are calculating BMI for anyone under the age of 20, use a BMI chart designed for young boys or girls. Their BMI numbers tend to be lower across the board than a traditional BMI scale.
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