How to Calculate BMI Using an Equation

Written by charlotte johnson
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BMI stands for "Body Mass Index." This measurement gives indications about the amount of body fat a person has and also suggests whether or not he or she is within a healthy weight range. You can use a simple BMI equation to figure out which of the following categories you fall into: (1) Underweight-- your BMI is less than 18.5; (2) Normal weight--your BMI equals 18.5 to 24.9; (3) Overweight--your BMI measures 25 to 29.9; and (4) Obese--your BMI is 30 or above.

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Things you need

  • Your weight and height; calculator (optional)

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  1. 1

    Determine which formula you will use. The equation that uses standard American measurement units is this:

    BMI = (weight in pounds x 703 ) / height in inches ²

    The metric formula looks like this:

    BMI = weight in kilograms / height in meters ²

  2. 2

    Perform the necessary mathematics using your weight. For instance, if you weigh 160 pounds, you would multiply that number times 703, giving you a result of 112,480. The metric equivalent of 160 pounds is 72.7 kilograms. If you're using the metric equation, you don't mutliply kilograms by the number 703; you just leave the kilograms figure (72.7) as is until you get to step 3.

  3. 3

    Complete the calculations using your height. If you are five-feet-nine-inches tall, this would convert to a total of 69 inches (12 inches in a foot). Now you must square this number:

    69 x 69 = 4761.

    In the metric formula, 69 inches would equal 1.75 meters. Perform the following equation if you are using the metric formula:

    1.75 x 1.75 = 3.06

  4. 4

    Divide the top figure by the bottom figure. Using the previous example, here's the American equation:

    112,480 / 4761 = 23.63

    If you're using the metric formula, your figures would look like this:

    72.7 / 3.06 = 23.76

    Note: The slight variation in the answers will not affect the final categorisation.

  5. 5

    Determine the category in which your answer lies. In this example, an individual with a BMI of 23.76 would be classified as normal weight. If your score places you in the underweight, overweight, or obese categories, you may wish to talk with your doctor about a diet and exercise plan that can help you reach your ideal physical condition.

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