The body mass index (BMI) is a number calculated from a person’s weight and height. The BMI is calculated by dividing the body mass by the square of the body height, and it is always expressed in kilograms per square meter (kg/m2), with mass in kilograms and height in meters.

The BMI can be calculated using a table or chart that shows BMI as a function of mass and height, with contour lines or colors for different BMI categories and other units of measurement (converted to metric units for the calculation).

[bmi-calculator]

Following are the weight categories used to calculate BMI:

BMI (kg/m)^{2} | Weight Range |

< 18.5 | Underweight |

18.5-24.9 | Healthy Weight |

25.0-29.9 | Overweight |

30.0 or higher | Obese |

## Obesity and Body Mass Index (BMI)

Between 1830 and 1850, Adolphe Quetelet, a Belgian astronomer, mathematician, statistician, and sociologist, constructed what he dubbed “social physics” and devised the BMI’s foundation. Ancel Keys and colleagues invented the term “body mass index” (BMI) to describe the ratio of human body weight to squared height in a paper published in the Journal of Chronic Diseases in July 1972. In this work, Keys stated that the BMI was “…at least as excellent as any other relative weight index as a predictor of relative obesity, if not totally satisfactory.”

The desire for a body fat index arose in response to rising obesity rates in developed Western societies. BMI, according to Keys, is appropriate for population studies but not for individual evaluation. Despite this, it has become frequently utilized for preliminary diagnostics due to its simplicity. Additional measurements, such as waist circumference, can be beneficial.

The BMI is calculated by multiplying the weight in kilograms by the height in meters. If pounds and inches are employed, a 703 (kg/m2)/(lb/in2) conversion factor must be used. The units are generally omitted when the word BMI is used casually.

BMI is a basic numeric measure of a person’s thickness or thinness that allows health practitioners to address weight issues with their patients more objectively. BMI was created as a simple way to categorize average sedentary (physically inactive) populations with a similar body composition. As of 2014, the following are value recommendations for such individuals: A BMI of 18.5 to 25 kg/m2 may represent appropriate weight, while a BMI of less than 18.5 indicates underweight, a figure of 25 to 30 indicates overweight, and a number of 30 or more indicates obesity. Male athletes with a high muscle-to-fat ratio have a BMI that is misleadingly high in comparison to their body fat proportion.

## How is BMI calculated?

It’s as easy as entering your height and weight into an online BMI calculator for women and men, similar to the ones given by the National Heart, Lung, and Blood Institute in the United States.

**BMI formula**: weight (in kilograms) divided by height squared (in meters), expressed as kg/m2.

- Formula: Weight (kg)/[height (m)]2

- Example: weight = 60 kg and height = 1.50 m

- Calculation: 60/ (1.50)2= 60/2.25=26.67

In the English System, it is calculated as follows: your weight (in pounds) divided by height squared (in inches) multiplied by 703.

- Formula: [Weight (lb)/height (in)]2 x 703

- Example: weight = 180 lb and height = 68 in

- Calculation: [180/ (68)2] x 703= [180/4624] x 703= 27.37

## BMI percentiles for girls aged 2 to 20 years old.

Children’s BMI is calculated differently. It’s calculated the same way it is for adults but then compared to usual values for other kids their age. Instead of being compared to predefined underweight and overweight standards, the BMI is compared to percentiles for children of the same sex and age.

Underweight people have a BMI of less than the 5th percentile, while obese people have a BMI of more than the 95th percentile. Overweight children are those who have a BMI between the 85th and 95th percentile.

According to recent studies in the United Kingdom, ladies aged 12 to 16 have a BMI that is 1.0 kg/m2 greater than boys of the same age.

### International Variations

These proposed linear scale distinctions might change over time and from nation to country, making global, longitudinal surveys difficult. People of various ethnic groups, populations, and descent have different associations between BMI, body fat percentage, and health risks, with a higher risk of type 2 diabetes mellitus and atherosclerotic cardiovascular disease at BMIs lower than the WHO cut-off point for overweight, 25 kg/m2, though the cut-off for observed risk varies among different populations. In both Europe and Asia, the observed risk cut-off differs depending on demographics and subpopulations.

### United States

The National Institutes of Health and the Centers for Disease Control and Prevention lowered the normal/overweight cut-off from BMI 27.8 to BMI 25 in 1998, bringing US criteria in line with World Health Organization norms. As a result, about 29 million formerly healthy Americans were reclassified as overweight.

This may explain why, during the last 20 years, the number of overweight people has increased, as has the number of people buying weight-loss products. WHO also advises reducing the normal/overweight threshold for southeast Asian body types to about BMI 23, with more adjustments expected when clinical trials of other body types are completed.

According to the 2015-2016 National Health and Nutrition Examination Survey, 71.6 percent of men and women in the United States have a BMI of over 25. Obesity, defined as a BMI of 30 or more, was detected in 39.8% of US adults. According to a 2007 poll, 63 percent of Americans are overweight or obese, with 26% being obese (a BMI of 30 or more). In 2014, 37.7% of adults in the United States were obese, with 35.0 percent of men and 40.4 percent of women falling into this category; class 3 obesity (BMI above 40) was 7.7% for men and 9.9% for women.

BMI figures for males and females aged 20 and up, as well as chosen percentiles by age, for the years 2011–2014 in the United States.