Figuring out your Body Mass Index (BMI) lets you compare your height and weight to get a rough idea of how much fat you're carrying on your body. According to the Centers for Disease Control (CDC), BMI is usually a reliable indicator of body fat; however, particularly fit, muscular individuals may have unusually high BMIs because the test cannot distinguish between weight from muscle and weight from fat.
BMI for children is computed with the same formula as an adult's BMI, but must be interpreted with the aid of growth charts since the amount of fat on a child's body differs with gender and with age.
Step 1
Weigh yourself and measure your height with the most accurate facilities at your disposal. A doctor's scale is best, although many home digital scales give reliable, accurate readings as well. For height, you can have a friend mark your height against a wall as you stand barefoot, then measure from the floor up to the mark. Make sure to record your weight in pounds and your height in inches.
Step 2
Square your height; that is, multiply it by itself. If you are 5 feet 6 inches tall, for example, first convert the feet-and-inches measurement to inches alone, or in this case, 66 inches. Multiply 66 by itself, which is 4,356.
Step 3
Divide your weight in pounds by the result from Step 2. For someone who is 5 feet 6 inches tall and weighs 150 pounds, for example, divide 150 by 4,356 for a result of .034435.
Step 4
Multiply the result from Step 3 by 703. In our example, this yields a result of 24.207, which we round to 24.21. This is the BMI for our example subject.
Step 5
Interpret the BMI to determine whether you are ranked underweight, normal, overweight or obese. According to the CDC, our example subject with a BMI of 24.21 is in the very upper limit of the normal range. Below 18.5 is considered underweight, from 18.5 to 24.9 is normal, from 25.0 to 29.9 is overweight and anything above that is considered obese.
Step 6
Consult a BMI-for-age chart if the subject is between 2 and 20 years of age. Make sure you use the gender-appropriate chart. Read across the bottom of the chart to the subject's age, then up to the subject's BMI, and then note which percentile line this falls on. According to the CDC, under the 5th percentile is considered underweight, between the 5th and 85th percentiles is healthy, from the 85th to the 95th percentile is overweight and above the 95th percentile is obese.
Things You'll Need
- Weight scale
- Measuring tape
- Calculator
Member Comments