Unifying Concepts

Body Mass Index (BMI) Calculator

BMI is body weight divided by a power of height, usually (height)2, which is said to be independent of stature. Calculations based on values for ideal body weight suggest that BMIs for normal men and women should be in the range of 18.5 to 25 kg/m2. Indeed, this range roughly corresponds to the 10th to 75th percentile values recorded from adult individuals. For infants and children, average BMI values change with age, from 13 kg/m2 at birth, to a peak of 18 at about 1 year, a nadir of 15 at about age 6 years, and then a rise to adult values during adolescence.

Individuals with high indices are classified as overweight, even obese, and those with subnormal indices as undernourished. However, such classifications cannot be applied, for example, to short muscular men or to tall asthenic women, and despite the sex difference in body fat, the average index is about the same for both sexes during the adolescent and young adult years.

WHO Classification of BMI
<18.5 Underweight
18.5-24.9 Normal
25-29.9 Overweight
30-34.9 Class I Obesity
35-39.9 Class II Obesity
>40 Class III Obesity

Usage Instructions: To calculate your BMI, enter your weight in pounds in the box. Next, enter your height in inches. Click on the ‘Submit’ button, and your BMI score and class will appear.

Your BMI is



  1. Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults–The Evidence Report. National Institutes of Health. Obes Res. 1998 Sep;6 Suppl 2:51S-209S. [Medline]
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