BMI Calculator

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Measurement System






What is body mass index (BMI)?

Body Mass Index (BMI) is a simple calculation using a person’s height and weight to categorize their relative level of obesity. It’s a useful tool for medical professionals to determine an individual’s weight category and whether that puts them at risk for specific health issues.

A Belgian scientist named Adolphe Quetelet developed the metric in the early 1800s as a means of gauging an individual’s relative body fat. He created the metric after observing an increase in obesity in Western society. The term Body Mass Index was first coined in a paper published in the Journal of Chronic Diseases in the 1970s. Since it was developed, medical professionals have used it as a simple way to categorize a person’s average body composition. Studies have shown that BMI levels can be correlated with body fat and correspond to future health issues and risks.

How BMI is Calculated

To calculate BMI, you merely take an individual’s weight and divide it by the square of their height (kg/m2). The result then falls into one of seven categories for different body compositions.

The Limitations of BMI

The World Health Organization (WHO) created the categories above. These categories are used as very relative measures. The WHO views any person with a BMI of 18 or less as underweight. Lower than 18 may indicate malnutrition, an eating disorder, or potentially other health issues. Between 18 and 25 is considered healthy weight and body composition. A BMI of 25 or higher is deemed to be overweight, while above 30 is considered obese. These values can only be used as general statistical categories and are not specific indications of any particular issue. Below we discuss the limitations and issues with the Index.

How BMI is Used

Though the BMI tool can be useful, there are certain factors and limitations for practitioners to consider. First, because this tool measures excess weight and not actual body fat it can be misleading in some populations including children, the elderly, the infirm, and athletes. BMI does not measure body density, fat, or muscle, simply a person’s weight relative to their height.

Below are some examples where BMI may not be an accurate reflection of a person’s body composition or future health risks.

  • Highly trained athletes or body-builders have BMIs that are often high and would generally fall into the obesity or overweight range due to their increased muscle mass.
  • Women, on average, tend to have more significant amounts of body fat than men with the same BMI
  • Older adults and the elderly tend to have higher amounts of body fat than younger adults with the same BMI
  • BMI is relatively inaccurate in children and adolescents due to a variety of factors including but not limited to: height, sexual maturation, fat-free mass, etc.

The Body Mass Index is a useful general tool for professionals to use because it is a cheap and simple way to gauge a broad picture of a patient’s relative health. Though it shouldn’t be used as a diagnostic tool since it doesn’t directly measure body fat. BMI is best used as a tool for tracking general weight statistics in the general population and to screen individuals for potential weight problems.

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