body mass index

The body mass index is a calculated numerical index which compares the ratio of weight to height and gives a quantified answer to the question of whether an individual is underweight, of normal weight, or overweight. I get asked about it from time to time; I am posting it here for reference (including my own). One way to calculate it is by the following formula. You will need to remember that

pounds times 0.45 = kilograms
inches divided by 39 = meters

The formula: BMI = weight (kg) / height²(m²)

General guidelines for BMI in older adolescents appear in the table below:

BMI % Ideal Body Mass
17 75%

18 85%

20-26 "Normal"

27-35 120-135%

35-42 135-200%

over 42 over 200%

If you have Javascript enabled on your browser, you can save yourself the trouble of calculating your BMI with a calculator, at least for older children and adults. The automatic calculator below does not accept heights under 48 inces or weights under 35 pounds. For those children, use the formulas below.

Free JavaScripts provided
by The JavaScript Source

A more general and accurate solution is now possible for use earlier in life. Since the growth pattern that a child is in by about 8 years of age tends to persist into adulthood, early measurement of the BMI is desirable in order to say more accurately a child's potential for obesity in adulthood.

To use BMI for younger children, first calculate the BMI using this formula:

BMI = weight (lb) / height²(in²) X 703

Where weight is expressed as pounds and decimal fractions (42 pounds 4 ounces is thus 42.25 pounds) and height is expressed as inches and decimal fractions (44-1/2 inches is thus 44.5 inches).

Then you (or your doctor) must plot the resulting number value of BMI on the new charts for boys (76K Acrobat file) and girls (77K Acrobat file). This procedure will work for any child or adolescent from 2 to 20 years old.

Those individuals who plot out between the 85th and 95th percentiles are defined as overweight. Those whose BMI lies at or above the 95th percentile are by definition obese.

If your child lies in the zone above the 85th percentile, it would be very advisable to talk to your child's doctor about dietary changes you can make and strategies to increase your child's exercise level.

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