The Connection Between BMI Numbers and Obesity Levels

An individual's weight and height are used to compute their body mass index (BMI). The BMI is summed by dividing the squared value of the person's height by the body weight. It is represented in kilograms per square meter (kg/m2). The BMI can be totalled by operating through a table or diagram that plots BMI as a ratio of size and mass utilizing shades to separate various BMI classes and may utilize different measurement units.

With rising obesity rates in affluent Western nations, there has been research on such a scale that quantifies body fat. BMI was categorically deemed by Keys to be acceptable for population research but unfit for the assessment phase. Yet, it is often utilized for first diagnosis because it is easy to use. Waist measurement is one additional statistic that may be helpful.

As weight = kilograms and height = meters, the BMI is given in kilograms per square meter (kg/m2). If pounds and inches are utilized, a conversion factor = 703 (kg/m2) or (lb/in2) is employed. The units are often left out when the word "BMI" is used casually.

How to Calculate BMI?

BMI = Mass (in kg)/ Height 2 (in metres) = (Mass (in lb) x 703) / Height 2 (in inches)

Nowadays, there are online BMI calculators that find your BMI easily if you put in the correct details about your body. However, consider that children between 2 – 19 years of age have different BMI calculators and adults, i.e., individuals 20 years or above, have adult BMI Calculators.

Need of BMI index

The BMI is indeed a helpful tool for gauging overweight and obesity in a demographic. Every adult, regardless of age or gender, uses it in the same way. To determine how well BMI can predict adiposity, researchers have looked at the link between BMI and the percentage of body fat (BF%) in various ethnic groups. With a sample of South Asian individuals with a different physical structure than currently researched ethnic groups, scientists investigated the link between BMI and BF%. They found them quite different from Europeans and East Asians. To determine if this connection is linear or curved, researchers looked at the effects of age and gender.

Nonetheless, BMI is not infallible. Today's experts advise against using BMI as a diagnosis; they advise using it as a diagnostic method to determine if you are overweight or obese. BMI should be considered as one aspect among several variables your doctor considers when determining your amount of body fat and general health rather than as the only one.

Classifications and Groups

According to the WHO, an adult with less than 18.5 BMI is considered underweight and may be a sign of malnourishment, chronic eating disorders, or other medical conditions. In contrast, a BMI of 25 or more is considered overweight, while a BMI of 30 or more is considered obese. Four different cut-off values for at-risk Asians (23, 27.5, 32.5, and 37.5) were found in addition to the standard global WHO BMI split points (16, 17, 18.5, 25, 30, 35, and 40). These BMI value limits are only reliable as statistical categories.

CATEGORY BMI (in kg/m2)
Underweight (Class III) < 16.0
Underweight (Class II) 16.0 - 16.9
Underweight (Class I) 17.0 - 18.4
Normal 18.5 - 24.9
Overweight 25.0 - 29.9
Obesity (Class I) 30.0 - 34.9
Obesity (Class II) 35.0 - 39.9
Severe Obesity (Class III) >= 40

If you find these figurines too confusing to understand here is a simple format for you −

  • BMI under 18.5 indicates being underweight.

  • BMI of 18.5 to 24.9 equals a healthy weight.

  • BMI of 25.0 to 29.9 indicates obesity.

  • Obesity if BMI is 30.0 or greater.

  • Morbidly obese at a BMI of 40 or above.

The BMI is applied differently to adolescents and children. Similar to adults, it is computed, and the results are then contrasted with those of similar-aged children or youth to determine normal values. The BMI is evaluated to percentiles of children of the same age and gender rather than predetermined standards for being underweight and overweight.

Does a high BMI only Indicate Obesity?

Simply put, no. The most straightforward approach to determine if an individual is overweight or obese is likely to be their BMI, but it's not the only method available. Other reliable measures of obesity include the waist-to-hip ratio and waist measurement. Each of these puts a lot of attention on visceral fat, which is hazardous abdominal fat.

Obesity is described by the World Health Organization (WHO) as a waist-to-hip ratio that is more than 0.85 for women and 0.9 for males. The formula for determining this is to divide the waist circumference by the pelvic measurements taken at the broadest portion of the buttocks.


The fact that BMI is affordable and straightforward is one of its main benefits. It is a measurement that can be determined for all trustworthy, non-invasive, and consistent populations. Nevertheless, using BMI alone to determine healthy weight measures does have some limitations, and its precision has recently come under scrutiny. BMI is not an optimum choice, and doctors advise against using it exclusively because it only provides a partial view of one's fitness. It doesn't consider a person's gender, ethnicity, age, muscle mass, body fat distribution, or kind of body fat.

There is no method to discern between muscle and body fat when using BMI alone to determine obesity, which is one of the main problems. When they are in excellent health, athletes and persons with a significant muscle mass could be considered obese, even if they do not have the same health concerns as people with a high-fat mass.

Fun Facts

  • With the same BMI, women frequently have greater body fat than males do.

  • With the same BMI, older individuals often have fewer muscles than younger individuals and more concentration of body fat.

  • Athletes, both professional and amateur, might have a higher BMI due to increased muscle mass rather than excess body fat.

  • Asians have a higher body fat percentage than non-Asians.

Alternate ways to Diagnose Obesity

  • Using callipers, measure the thickness of a skinfold.

  • Weighing when underwater.

  • Bioelectric impedance test.

  • Dual-energy X-ray Absorption measurement (DXA).


The BMI shouldn't be used to estimate body fat mass any longer. However, the classifications and standards should be updated to reflect the current variety in BMIs worldwide if BMI is to be used indefinitely.

It would be nice to have a technique for measuring body fat percentage and its link with various illnesses and deaths more precisely than the BMI.

The BMI was not initially created as a measure of fatness for use in population-based investigations. It has, however, been appropriated for this use since it is simple to acquire measure. It is essential to realize that the BMI may include significant limitations when measuring the percentage of body fat mass. It could be deceptive in this sense, especially for guys. Furthermore, biassed language is now being employed. In Western, developed countries, it is considered the norm for at least half of adults to be overweight (preobese) or obese.

Updated on: 02-Mar-2023


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