Body mass index (BMI) is a simple diagnostic formula used to estimate a person's fatness or thinness relative to her height. BMI is commonly used in the diagnosis of obesity and eating disorders.
Formula
The formula for calculating body mass index is written as weight in kilograms, divided by the square of the person's height in meters.
Normal Range
The World Health Organization defines a normal BMI as lying between 18.5 and 24.9. This range may differ slightly between nations due to cultural differences and ethnic variations of body type.
Significance
While BMI can't accurately estimate a person's overall health, it is used by most medical practitioners to gauge a patient's ideal body weight and his target weight-range.
Considerations
The BMI formula is a fairly crude diagnostic tool and does not account for sex, muscle mass, age, ethnicity or body fat distribution.
Sub-Categories
Patients with a BMI of 25 or more are considered to be overweight; this may be further classified into the categories of pre-obese, obese class I, obese class II and obese class III. Sub-categories of underweight (less than 18.5) are used in nations where undernutrition is common.
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