A Basic Body Mass Index Definition

The body mass index definition states that it does not actually measure the percentage of body fat, a common misperception, but instead simply determines if you are a healthy weight for your height. If you are concerned about your weight, the body mass index (BMI) tool is very helpful in determining whether you are underweight, overweight or obese.

What is the BMI?

Developed sometime between 1830 and 1850 by Dutch scientist Adolphe Quetelet, the tool is sometimes also called the Quetelet index. Because it is very easy to calculate, it is currently the most widely used and accepted form of measurement to determine weight problems for both children and adults.

The body mass index formula is an individual’s body weight divided by the square of his/her height. Because the formula was originally developed in metric units, to use with pounds the correct formula is:

BMI = weight (pounds) x 703

Height2 (inches2)

What is a Healthy BMI?

By using this calculation, the optimal BMI would be anywhere between 18.5 and 25. If your figure is lower than 18.5 you would be considered underweight, while if you where over 25 you would be overweight. A number over 30 is considered obese, while over 40 is morbidly obese.

How are BMI Calculations Used?

BMI calculations are primarily used for recording statistical information on the obesity of the population and determining patients with risk factors for obesity-related health problems. However, these numbers do not take into account many factors that can also affect weight, such as frame size and muscularity.

The tool is very easy to use and can be done quickly without any expensive equipment, making it an ideal choice for a clinical setting. It is also commonly used to determine rates for health insurance coverage, as higher BMIs have been associated with more illness and on-going health problems.

How Reliable is BMI?

The results for BMI are very strongly correlated with overall health. There are varying results and thresholds based on sex, race, and age. These include:

  • With the same BMI, women generally have more body fat than men
  • With the same BMI, older people generally have more body fat than younger adults
  • Elite athletes tend to have high BMIs because of increased muscle mass, not increased body fatness

There are often other factors that are associated with risk for disease. Two other heavy predictors are:

  • Waist circumference: abdominal fat is a good predictor of an individual’s risk for obesity-related diseases.
  • High blood pressure and lack of physical activity can contribute to risk for diseases and conditions associated with obesity.

Talk to your doctor to determine if your weight is in a healthy range, and seek advice on the best way to lose weight if your BMI calculations (and doctor’s advice) deem it necessary.


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