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# Body Mass Index Calculator

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## What is Body Mass Index (BMI)?

The body mass index (BMI) is a value calculated from the mass (weight) and height of an individual. The BMI formula is defined as the body mass (in kilograms) divided by the square of height (in metres) and is expressed in units of kg/m2.

The BMI calculator is an attempt to quantify the amount of tissue mass (muscle, fat, and bone) in an individual, and then categorize that person as underweight, normal weight, overweight, or obese based on that value.

The BMI formula when using inches and pounds the same as for metric but the result is multiplied by 703.

## History of the BMI

A Belgian astronomer, mathematician, statistician and sociologist, Adolphe Quetelet, devised the basis of the what is currently known as the Body Mass Index between 1830 and 1850.

The modern term "body mass index" (BMI) was first used in a paper published in a 1972 edition of the Journal of Chronic Diseases by Ancel Keys and others.

After observing an increasing obesity in Western societies, Keys judged that the BMI was appropriate for population studies but inappropriate for individual evaluation. Despite this, because of its simple formula, it has come to be widely used for preliminary measurement of obesity.

The BMI is expressed in kg/m2, resulting from mass in kilograms and height in metres. If pounds and inches are used (lb/in2) the result must be multiplied by a factor of 703.

## Accuracy of a BMI Calculator

Should we be using the BMI calculator today as a measure of health and obesity levels?  The simple answer is a resounding NO.

In 2016 a study by UCLA concluded that "close to half of Americans who are considered "overweight" by virtue of their BMIs (47.4 percent, or 34.4 million people) are healthy, as are 19.8 million who are considered "obese."" The study also found that  "More than 30 percent of those with BMI's in the "normal" range - about 20.7 million people - are actually unhealthy based on their other health data.

More than 2 million people who are considered "very obese" by virtue of having a BMI of 35 or higher are actually healthy. That's about 15 percent of Americans who are classified as very obese."

There are many reasons why BMI is a poor measure of health, but one of the main ones is that BMI can’t distinguish between body fat and muscle.

This means that many fit, athletic, muscular people are incorrectly labeled as “overweight” by their BMI.

With no distinction between fat or muscle, levels of each can fluctuate wildly and have no overall effect on BMI.  Take for example two males with the same height and weight and thus same BMI, one who works out regularly and has high level of muscle and very low body fat, the other leads a sedentary lifestyle and has a high level of body fat and low level of muscle.  One of these males is very healthy, while the other is not, despite having the same BMI.

BMI also fall short as it doesn’t measure or take into account the location on the body where fat is stored.  Some individuals have skinny legs and carry most of their fat around their waist, while others may have the same amount of fat, but spread more evenly around the body.  Body fat stored Viscerally (around the organs) is the most dangerous of all types of fat.

Another problem with BMI is the lack of differentiation between male and female results.  The BMI for men is the same as the BMI for women with both being represented on a single BMI chart despite obvious physical differences.

In the following BMI charts comparing measured BMI with Body Fat Percentage results for males and females, each dot represents a single individual.  The lower right quadrant represents those tested with a BMI in the overweight and obese categories while Percent Body Fat is less than the upper normal range value of 20% for men and 28% for women.

Also take note of the upper left quadrant where the BMI is considered in the normal range (less than 25) yet the body fat percentages are above the normal range, even as high as 35% for one male and a staggering 43% for one female.

## BMI Vs Percent Body Fat - Men

Graph 1.0

Graph 1.0 above shows 29.9 % of males with a BMI greater than 25 have a body fat percentage of less than 20% (lower right quadrant). Total men measured in graph was 16,990 on an InBody 570.

## BMI Vs Percent Body Fat - Women

Graph 1.1

Graph 1.1 shows that there is a larger portion of females who are in the normal range for BMI (<25) but carry significant percentages of body fat. (Upper left quadrant).  Total females measured was 30,740  on an InBody 570.

## Better alternatives to using BMI

The inaccuracy of BMI has led many to try to develop far more accurate measurements of obesity.

Waist to hip ratio, the ratio of waist measurement compared to that of the hip measurement, has been argued by many to be a much better alternative than BMI.   According to the World Health Organisation, this measurement should be no more than 0.85 for women and 0.9 for men.  The benefit of this measure is that it looks at your fat placement around the midsection which often can be the most cause for concern.

Jocelyn Wynd, the director and founder of Melbourne Body Composition Analysis, believes that the most accurate way of assessing levels of obesity and health is by splitting the BMI into a fat portion and a lean portion via body composition analysis.  Comparing the level of just body fat and lean mass relative to height yields calculations called the Fat Mass Index (FMI) and Fat Free Mass Index (FFMI).  The FMI can also be categorised into separate male and female charts.

The main benefit of using FMI and FFMI is that unlike BMI calculation and body fat percentage, a change in muscle will not affect the FMI and a change in body fat will not affect the FFMI.

FMI is calculated by dividing the Fat Mass in Kilograms by the square of the height (in metres).

A body composition analysis is required to obtained an accurate reading of Body Fat Mass for this method.

The chart below show the ranges for FMI for males and females.

Fat Mass Index Classification of Ranges