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What Is My BMI?

When it comes to defining the word "obesity," the BMI, or Body Mass Index, is an important number. Your BMI number allows you to see how you compare to the average healthy individual, and gives you the information you need to encourage a healthy exercise program and diet regimen. Calculating your BMI is quick and easy, and in most cases all you need is your height and weight measurements.

  1. What It Is

    • The Body Mass Index is a number calculated from a person's height in relation to her weight. Once these numbers are inserted into the BMI formula, they give a semi-accurate prediction of the level of fat in the body. Though not as accurate as energy X-rays or water weighing, BMI still works as a way to estimate body fat. BMI calculation is also free and available to everyone, unlike other methods that can be expensive.

    How It's Used

    • BMI is a screening method to help determine the level of obesity in an individual, and therefore his risk of weight-related health problems. A high BMI does not guarantee that an individual is going to have health issues, but it does give him a reason to get a full checkup by a doctor. The doctor will confirm the results of the BMI number by performing skin-fold tests and physical-activity testing, as well as a full investigation of the patient's diet and exercise habits. If the doctor finds any health risk, she will prescribe appropriate diet and exercise routines to help the individual lower his BMI.

    Calculation

    • BMI is calculated by dividing your weight in kilograms by your height in meters squared. Since height is normally measured in centimeters, you can divide your height by 100 to get your height in meters for the equation. (For an automatic BMI calculator, follow the link in Resources.)

    Link to Obesity

    • Once the numbers have been calculated, the BMI number can be compared against a BMI chart to to measure obesity. The numbers on a BMI chart start at 18 and stop at 30. A BMI of 18.5 or lower is considered underweight. A BMI 18.5 to 24.9 is normal. A BMI of 25.0 to 29.9 is considered overweight, and a BMI of 30 and above is considered obese.

    BMI in Children and Teens

    • Computing BMI in the manner explained above only works for people 20 years and older. For those under the age of 20, a separate BMI chart is used. The BMI calculation for teens also takes into account age and sex--largely because children and teenagers are still growing, as well as going through puberty. This causes drastic changes in BMI, depending on their age and gender. (A link to a BMI calculator for children and teens can be found in the Resources section.)

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