Body Mass Index
Percentage of Body Fat

Body Mass Index (BMI) is a reliable indicator of body fatness for people without measuring body fat directly as an inexpensive and easy-to-perform method of screening for weight categories that may lead to health problems.

BMI is a measure which takes into accounts a person's weight and height to gauge total body fat in adults, and for children when age and sex percentiles are used.

Someone with a BMI of 25 to 27 is about 20 percent overweight, which is believed to carry moderate health risks. A BMI of 30 and higher is considered obese, with the higher the BMI, the greater the risk of developing health problems.

Heart disease, diabetes and high blood pressure are all linked to being overweight. BMI is one of the most accurate ways to determine when extra pounds translate into health risks.


The correlation between the body mass index number and body fat is fairly strong; however the correlation varies by sex, race, and age. Some examples of these variations are:

  • At the same BMI, women tend to have more body fat than men.
  • At the same BMI, older people, on average, tend to have more body fat than younger adults.
  • Highly trained athletes may have a high BMI because of increased muscularity rather than increased body fatness.

    It is also important to remember that BMI is only one factor related to risk for disease and assessing someone's as being overweight or obese. Other factors to consider are:

    • The individual's waist circumference (because abdominal fat is a predictor of risk for obesity-related diseases).
    • Other risk factors the individual has for diseases and conditions associated with obesity (for example, high blood pressure or physical inactivity.


    To calculate your body mass index:

    • Take your weight in kilograms
    • Divide that number by your height in meters(squared)
    • If you use pounds and inches instead, multiply the number you get by 704 to get your final BMI
    • 19-24.9 = you are fit
    • 25-29.9 = overweight
    • 30 and over = Obese

    For example:

    • If you weigh 123 pounds and are 64 inches tall
    • 123 divided by 4,096 (64 squared) = .030029 X 704 = BMI of 21.14
    • You are fit

    Of course, like anything else, an easier way to do the math is by using a BMI calculator, or a table as below.

    To use the table, find the appropriate height in the left-hand column and move across to your weight.


    It is not appropriate to use the body mass index categories for adults to interpret BMI numbers for children and teens without using age and sex percentile.

    Healthy weight ranges change with each month of age for each sex and as height increases for children.

    Although BMI is used to screen for overweight in children and teens, it is not a diagnostic tool. Further assessment might be needed, such as skin fold thickness measurements.

  • Always consult your health care professional before making any changes in your diet or exercise regime. You doctor can help determine a counseling strategy, assessments of diet, health, and physical activity needed.

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