BMI, or body mass index, is a number calculated from a person's height and weight. BMI is generally reliable in telling a person's body composition, though it does have problems with populations like athletes and bodybuilders. Although it is not a direct measurement of fat, there is a strong correlation to a person's Z score (the name of the number produced by the calculation) and actual body fat percentages. BMI is used because it is a quick, easy, noninvasive and inexpensive way for clinicians and the general public to assess body compositions.
Calculating BMI
Step 1
Measure your height accurately. Many people overestimate their height by as much as an inch. The purpose of calculating your BMI is to get an accurate assessment of your body composition. This requires figures to be accurate.
Step 2
Calculate your height in inches squared. If you are 5 feet 10 inches, you are 70 inches tall; 70 inches squared is 4,900.
Step 3
Stand on a weight scale. Multiply your weight in pounds by 703. If you weigh 190 lb., this number would be 133,570.
Step 4
Divide the above number by your height in inches squared to get your Z score. In this example, 133,570 divided by 4,900 is 27.26. Review the chart in Tips to see where your Z score ranks.
Tips and Warnings
- The equation for BMI is weight in pounds multiplied by 703. Divided by height in inches squared. A score under 18.5 is underweight. A score between 18.5 and 24.9 is normal. A score between 25 and 29.9 is overweight. A score above 30 is obese.
Things You'll Need
- Weight scale
- Calculator
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