A body mass index (BMI) is a number that compares your height with your weight. The World Health Organization (WHO) uses it in population studies to classify the weight of people in a population group. The BMI is therefore important for identifying population groups that may be underweight or overweight. The BMI can be calculated quickly because it only requires you to measure height and weight, making it convenient for use on large groups. Many people also use it for individual diagnosis, although this is an inappropriate use of the BMI. A child's BMI may also be used as a preliminary screening tool to identify children who may be severely underweight or overweight. This use of the BMI compares a child's BMI to those of other children of the same age and gender.
Step 1
Obtain the subject's weight with a scale. The WHO BMI chart requires the weight to be in kilograms. Divide the subject's weight in pounds by 2.2 to obtain the weight in kilograms.
Step 2
Measure the subject's height with a tape measure. The WHO BMI chart requires the height to be in meters. Multiply the subject's height in inches by 0.0254 to obtain the height in meters.
Step 3
Compute the subject's BMI as w / (h x h) where w is the subject's weight in kilograms and h is the subject's height in meters. Use this BMI value and a BMI reference chart to determine the subject's weight classification.
Step 4
Identify underweight classifications. According to WHO, a BMI below 18.50 is classified as underweight. A BMI below 16 indicates the subject is severely underweight, a BMI in the range of 16 to 17 indicates the subject is moderately underweight and a BMI in the range of 17 to 18.5 indicates the subject is mildly underweight.
Step 5
Determine normal BMI values. The range for normal BMI values is between 18.5 and 25. A BMI in the range of 25 to 30 indicates pre-obesity.
Step 6
Classify BMI values indicating obesity. A BMI in the range of 30 to 35 indicates obese class I. A BMI in the range of 35 to 40 indicates obese class II. A BMI greater than 40 indicates obese class III.
Things You'll Need
- Scale
- Tape measure
- Calculator
- BMI chart
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