BMI Calculator

Body mass index (BMI) is a measure of body fat based on height and weight that applies to men and women. BMI calculator for women and men provides body mass index (BMI) and the corresponding BMI weight status category for adults 20 years and older.

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BMI calculation

BMI in an individual is calculated by the use of a mathematical formula. It can also be estimated using tables in which one can match height in inches to weight in pounds to estimate BMI. There are convenient calculators available on internet sites that help calculate BMI as well.

The formula is - BMI = (Weight in kilograms) divided by (Height in metres squared)

A normal BMI score is one that falls between 18.5 and 24.9. This indicates that a person is within the normal weight range for his or her height. A BMI chart is used to categorize a person as underweight, normal, overweight, or obese.

BMI is proportional to the mass and inversely proportional to the square of the height. So, if all body dimensions double, and mass scales naturally with the cube of the height, then BMI doubles instead of remaining the same. This results in taller people having a reported BMI that is uncharacteristically high, compared to their actual body fat levels. In comparison, the Ponderal index is based on the natural scaling of mass with the third power of the height.

However, many taller people are not just "scaled up" short people but tend to have narrower frames in proportion to their height. Carl Lavie has written that, "The B.M.I. tables are excellent for identifying obesity and body fat in large populations, but they are far less reliable for determining fatness in individuals."

Is BMI applicable for all?

For most people, BMI can be used to provide a good measure of obesity. But BMI fails to provide actual information on body composition like amount of muscle, bone, fat, and other tissues.

In some persons BMI is a more accurate measure of body fat than others. For example, persons who are very muscular may fall into the “overweight” category when they are actually healthy and very fit. These persons with a very low body fat percentage could have the same BMI score as someone who is overweight.

Similarly, an elderly and frail individual person may be in the normal weight category when they have little muscle mass and a high percentage of body fat.

BMI, when used for children and adolescents who are still growing, those with large body frames or petite builds, pregnant women and highly muscled individuals thus need to be assessed and interpreted carefully.