Articles in Weight Loss
Body Mass Index
Body Mass Index
Body Mass Index (BMI) is a number calculated from a person’s weight and height. BMI is a reliable indicator of body fatness for people.
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BMI does not measure body fat directly, but research has shown that BMI correlates to direct measures of body fat, such as underwater weighing and dual energy x-ray absorptiometry.
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BMI can be considered an alternative for direct measures of body fat.
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BMI is an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.
Calculation of BMI
BMI calculation is based on the following formulas:
Measurement units |
Formula and calculation |
Kilograms and meters (or centimeters) |
Formula: weight (kg) / [height (m)]2 Calculation: [weight (kg) / height (m) / height (m)]With the metric system, the formula for BMI is weight in kilograms divided by height in meters squared. Since height is commonly measured in centimeters, divide height in centimeters by 100 to obtain height in meters. Example: Height = 165 cm (1.65 m), Weight = 68 kg Calculation: 68 ÷ (1.65)2 = 24.98 |
Pounds and inches |
Formula: weight (lb) / [height (in)]2 x 703 Calculation: [weight (lb) / height (in) / height (in)] x 703Calculate BMI by dividing weight in pounds (lbs) by height in inches (in) squared and multiplying by a conversion factor of 703. Example: Weight = 150 lbs, Height = 5’5” (65") Calculation: [150 ÷ (65)2] x 703 = 24.96 |
Interpretation of BMI
For adults 20 years old and older, BMI is interpreted using standard weight status categories that are the same for all ages and for both men and women.
The standard weight status categories associated with BMI ranges for adults are shown in the following table.
BMI |
Weight Status |
Below 18.5 |
Underweight |
18.5 – 24.9 |
Normal |
25.0 – 29.9 |
Overweight |
30.0 and Above |
Obese |
The correlation between the BMI number and body fatness is fairly strong; however the correlation varies by sex, race, and age. These variations include the following examples:
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At the same BMI, women tend to have more body fat than men.
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At the same BMI, older people, on average, tend to have more body fat than younger adults.
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Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness.
