BMI Calculator

What is Body Mass Index (BMI)?

The Body Mass Index (BMI) is a simple screening tool used to categorize individuals into weight categories (underweight, normal weight, overweight, or obese) based on their height and weight. It is widely used by health professionals as a quick indicator of potential health risks related to body weight. It is also sometimes called the Quetelet index.

The BMI was invented by Adolphe Quetelet between 1830 and 1850. A scientist named Ancel Keys first used the term Body Mass Index in 1972. He wrote that governments should measure the BMI of adults to find out whether they are too fat or too thin.

How is BMI Calculated?

BMI is calculated using a straightforward formula:

For example, if you weigh 70 kg and are 1.75 meters (175 cm) tall, your BMI would be: .

BMI Categories and What They Mean

Health organizations, including the World Health Organisation (WHO), use these numbers for adults:

Some people disagree with these numbers. For example, some experts think the Overweight range for people with Asian body types should be 23–27.49, not 25–29.99. Some experts also think the lowest Normal BMI should be 20 for men, and 18 for women. The old BMI definition of overweight was 27; this changed in 1998.

Uses of BMI

BMI is particularly useful for governments who want to know about the health of their people. For example, in the United States in 2007, 74% of adults had a BMI above 25 (categorized as Overweight or Obese), and 27% of adults had a BMI above 30 (categorized as Obese). This information helps governments decide what public health initiatives to implement, as many of these individuals may become ill due to excess weight.

For individuals with "normal" bodies, BMI is a popular tool because it is easy to use and understand, and it provides useful general information.

Limitations of BMI

While a useful screening tool, BMI does not say how much weight is fat, how much is muscle, and how much is bone. It does not account for factors like body composition (muscle vs. fat), age, sex, or ethnic group. For instance, many athletes have a high BMI because they have lots of heavy muscle, not because they are fat. Conversely, other people might have lots of fat and not much muscle, appearing to be too fat even with a normal BMI. It\'s a general indicator, not a definitive health assessment.

When to Consult a Healthcare Professional

If your BMI is outside the normal range, it's recommended to consult a doctor or a qualified healthcare professional. They can provide a more comprehensive assessment of your health, considering your lifestyle, family history, and other health indicators, to give personalized advice.

Variations and Alternatives to BMI

The Ponderal Index is similar to the Body Mass Index, but the height is cubed, not squared. The formula is:

Some experts suggest that for the best formula, the exponent for height should be between 2.3 and 2.7.