Body Mass Index Formula

Is it possible to calculate your Body Mass Index (BMI)?

A person's BMI is calculated using the formula kilograms divided by height in meters squared. Weight classifications such as underweight, healthy weight, overweight, and obesity may be determined by a low-cost and easy screening test such as body mass index (BMI)

It is important to note that, although BMI is not a direct measure of body fat, it is only slightly related to more direct actions of body fat. Moreover, the BMI seems to be just as strongly related to a wide range of metabolic and disease outcomes as these more direct assessments of body fatness.

The Body Mass Index (BMI) of a person is computed by dividing the individual's kilograms by the square of their height in meters2. When one's BMI is high, it may indicate that one has a lot of body fat. However, BMI testing for weight categories does not assess individuals' body fatness and health, leading to health risks.

BMI Calculation

The procedure for calculating BMI in adults and children is the same. When doing the calculations, the following formulas are used.

Measurement UnitsFormula and Calculation
Kilograms and meters (or centimeters)

Weight (kg) / [height (m)] is the formula.

The formula for BMI in the metric system is weight in kilogrammes divided by height in metres squared. Height is generally measured in centimetres, and thus divide height in centimetres by 100 to get height in metres.

For instance, if your weight is 68 kilogrammes and your height is 165 centimetres, you would use the following formula: (1.65 m)

Calculation: 68 (1.65 + 24.98)2 = 24.98

There is a strong link between BMI and body fatness, even though two people with the same BMI may have different amounts of body fat.

Women, on average, have more body fat than men, even when both have the same body mass index.

Blacks have less body fat than Whites, and Asians have more body fat than Whites, even when they have the same BMI.

Compared to younger people with the same BMI, older people have more body fat.

Sportspeople with the same BMI as non-athletes have less body fat than the opposite.

When comparing those with larger BMI and body fatness, BMI is more accurate as a predictor of body fatness16. The BMI of a person who has a very high BMI (for example, 35 kg/m2) is particularly likely to have significant body fat. In contrast, a somewhat high BMI might have little body fat or a large amount of lean muscle mass (muscle and bone). A qualified healthcare practitioner should assess a person's health to determine their current health status and potential risks.

Trends in the BMI

Adults with a BMI greater than or equal to 30 kg/m2 (obesity) have increased considerably during the 1970s. However, except for older women, this trend has already stabilized. According to recent data, females above the age of 60 are becoming more obese.

For children, the BMI is calculated as follows:

Children and teens have a different interpretation of their BMI than adults, even though their BMI is calculated similarly to adults'. Because body fat changes with age and differs between girls and boys, the BMI of children and teens must be age and sex-specific. This variability is taken into consideration by the CDC BMI-for-age growth charts, which graphically portray BMI as a percentile grade. They were estimated using representative data from the United States population of 2- to 19-year-olds acquired from various surveys conducted between 1963 and 1965 and between 1988 and 1994.

In this reference sample from 1963 to 1994, obesity in children aged 2 to 19 is defined as having a body mass index (BMI) above the 95th percentile of children of the same age and gender. A BMI of 22.9 kg/m2 is usual for a 10-year-old child of typical height (56 inches) and weight (102 pounds). And this would place the kid in the 95th percentile for BMI, which implies that his BMI is greater than that of 95% of similarly aged boys in this reference group, and he would be classified as obese.

BMI for Adults

For adults, BMI is a measure of body mass index.

When calculating BMI for people above the age of 20, weight status categories are used that are more traditional. In addition, various body types and ages are included in these classes, which apply to both men and women.

The following weight classifications are available:

Under 18.5

18.5 – 24.9

25.0 – 29.9

30.0 and Above.


Healthy Weight



Aside from BMI, there are other methods of measuring body fatness. These include skinfold thickness measurements (with callipers), underwater weighing, bioelectrical impedance, dual-energy x-ray absorption (DXA), and isotope dilution 1,2,3. On the other hand, these techniques are not always easily accessible, and they are either costly or need the use of highly skilled personnel to complete. Many of these processes are also difficult to standardize across observers or computers, making comparisons across studies and periods more challenging.