Why BMI Is Not Accurate?


5 Min Read

Weight x .45 = A, Height (Inches) x 0.25 = B. BMI = A/B². The problem with BMI is that is doesn't account for your bone density, weight or muscle mass. Increasing muscle could increase your BMI, depending on your build. BMI may not be as accurate as other fat testing methods such as Dexa scans and hydraulic testing, which look for fat than mass.

Body Mass Index (BMI) is a way to measure whether or not a person is underweight, overweight or normal weight. It is a calculation that evaluates body mass compared to height. It is widely used to determine if people fall within a weight range that is healthy.

We are living in a time when people are more obsessed than ever in being thin.

The visual images put forth in the media are that of super skinny women and body builder men, which can make us normal people feel a bit self-conscious. Recently, a few actors and models have come forward to show the contrast between their photoshopped selves and what they look like before alteration. However, it is difficult to remember when we open a magazine that we are looking at an artistic creation, not a true reflection of the real world. A measurement like BMI can bring us back to reality with a more realistic assessment of what it means to be healthy. It can also enlighten us to the reality of weight problems. Having said that, BMI does have its limitations.

BMI is calculated by comparing weight in kilograms to height in centimeters. If you’re like me and live in the U.S., you probably have absolutely no clue whatsoever what your weight is in kilograms or what you measure in meters. I remember hearing as a child about how we were inevitably going to convert to the metric system, but I’m a fully grown adult and I’m still waiting. So before we get started, us Americans need to do a little extra calculating.

*First, we need to multiply our weight in pounds by .45.

So I weigh about 120 pounds (I think, Honestly, I only weight myself once a year when I go to the doctor’s office.) So, my first step would be to multiply 120 x .45 which equals 54 kg.

*Then we Americans have multiple our height in inches by .025.

I’m 5 foot, 5 inches, or 65 inches to be exact. So my calculation is 65x.025 which equals 1.625 m. Ok, now we are working with the metric system. Whew, that’s a lot of math, and we haven’t even gotten to the real equation yet!

The equation to determine BMI is weight divided by height squared.

So the first thing we need to do is determine our height squared. Back to using myself as an example, I’ll multiply my height by itself (1.625 x 1.625) which equals 2.64. And the final step is then to divide my weight (54) by my height squared (2.64). This means my BMI is 20.45.

Summary of the results as per the World Health Organization



Determine Your BMI

But here’s the catch. This evaluation doesn’t account for someone’s build. Is the person small boned, stocky or muscular? Having extra pounds of muscle is very different than having extra pounds of fat. Someone who gains weight by muscle lifting will have in increases in BMI, just as someone does who is sedentary and gaining fat. So BMI can be a helpful indicator of health for many, but it doesn’t tell the entire story for everyone. Therefore, it is important when calculating BMI to really evaluate someone’s build. We can quickly see that a body builder is not obese, but muscular. BMI does not evaluate and that is where BMI falls short

There are other, more accurate ways to evaluate body composition. One of the best ways is to measure body fat directly. Excess weight is usually only problematic when it is composed of fat. There are many ways to measure body fat. There is hydraulic testing which involves measuring fat by submerging a person in water. There are Dexa scans, which can also be used to measure bone density and evaluate risk for osteoporosis. A Dexa scan uses beams of light to determine body fat as well as bone density. These methods can give a very accurate reading, however, they also can cost a pretty penny. Skin Calipers are a cheaper method, often used in gyms to pinch the skin and take fat measurements. The skin calipers literally grab the skin and then measure the skin fold. This method is commonly used due to its convenience along with its low price tag. However, because fat is only measured in a few select areas, it is difficult to get a truly accurate reading of overall body fat this way.

For this reason, BMI remains one of the most commonly used measurements to determine body composition. No, it is not a perfect way to evaluate a person. BMI needs to be taken with a grain of salt, and a person needs to be honest with themselves in evaluating their own muscle mass. This can be difficult as, not only do people overestimate the amount of muscle they have, they also underestimate it. My suggestion when looking at a questionable BMI is to follow-up with skin calipers. BMI doesn’t create the entire picture of whether a person is healthy, but it is a convenient tool to start exploring the topic.

Erica Mesirov

Erica earned her Master’s Degree in holistic nutrition in 2014. She works with people who struggle with eating right or losing weight and know they want to be healthy, but their attempts have come up empty. By helping people understand their individual body and the imbalances that are causing unhealthy patterns, she gives people the opportunity to feel good about eating again.

Erica Mesirov

Erica earned her Master’s Degree in holistic nutrition in 2014. She works with people who struggle with eating right or losing weight and know they want to be healthy, but their attempts have come up empty. By helping people understand their individual body and the imbalances that are causing unhealthy patterns, she gives people the opportunity to feel good about eating again.

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alpha754293 5pts

@Erica Mesirov 

What makes you an "expert"?

The fact that your "about me" page says: "I specialize in helping people detox..."indicates to me that you're probably FARRR from being an expert.

Name a toxin that ISN'T processed by your hepatic and/or renal systems.

And the irony of your entire "article" (blog post) is that you complain about math, but then also complain about how this simple equation is insufficient to properly assess the health of a person based on some physical characteristics.

In other words, you want it to be a 2nd order PDE, but then complain that it's a 2nd order PDE. And I can only surmise that this inherent cognitive disconnect can only be missed by those that are irony impaired.

Christie-lee Knatt
Christie-lee Knatt 5pts

I know, your just one of the people I tag into all this stuff now lol

Luke Burles
Luke Burles 5pts

BMI is only one of about 4 tests I use

Luke Burles
Luke Burles 5pts

Yea it is an indication only. As it categorizes the world into 4 - 5 categories

Kevin Cischke
Kevin Cischke 5pts

Sadly the medical insurance models all use BMI. It's unfortunate

Dyana Galvan
Dyana Galvan 5pts

Because BMI calculation doesn't take into consideration muscle mass. :)

Onoskelis Bóveda
Onoskelis Bóveda 5pts

I don't care what my or my kids bmi is. I know what we eat and how much we move

Melissa Dalby
Melissa Dalby 5pts

They want everyone to be the same and what is idealistic to a chart despite genetic predispositions.

Ann Haha
Ann Haha 5pts

I wish there was some mention of the indication that people who have a healthy fat level live longer. Being super skinny, or very muscular does not equal being healthy and balanced. Having a percentage of body Fat is not a death sentence. I think the BMI is useless and is only used to make money by selling people sh*t they don't need. Imo

Chrissy Windley
Chrissy Windley 5pts

a few of my friends complain about weight and bmi because of their large breasts. your bmi/weight for your height is going to be off if you have extremely large breasts because it adds a lot of weight to your body and people don't understand that.

Jaqueline Castillo Fernández
Jaqueline Castillo Fernández 5pts

I think that in the middle of green and orange, should be another, i think im in the middle \U0001f62d\U0001f605

Rosalinde Czaja
Rosalinde Czaja 5pts

You're talking about a pinch test that estimates body fat. BMI is couculated with just your height and weight. BMI has nothing to do with body fat percentage or athletic fitness.

Rishika Subagh
Rishika Subagh 5pts

With more muscle the bmi is lower . I'm a trainer and I've done those measurements before. Someone with a lot of fat has huge BMI. Someone with muscle there's no way hardly to pinch any fat in the BMI skin and fat pincher.

Yolis Sandcer
Yolis Sandcer 5pts

5'5 137.lbs \U0001f4aa\U0001f44d\U0001f44d\U0001f44d\U0001f44d

Ash Sharma
Ash Sharma 5pts

It was never accurate because I have never met anyone who is within these limits

Ruth Nohemi Carral
Ruth Nohemi Carral 5pts

Thank you Aryuveda! I never learn or read about this before but I always thought I was different. I remember when I was younger I was always heavier there my friends but I looked thinner and they always thought that I was fatter then them, even though I wasn't..(you know kids cruelty) I also know as a common sense that some thing was not right. As I grow up I tell people that I always been heavier then I looked.

Janelle Yeomans
Janelle Yeomans 5pts

You can get special scales that measure with reasonable accuracy muscle/fat % They also use those in gyms along with BMI and waist measurement

Patresa Pfeifer
Patresa Pfeifer 5pts

Love this! I'm 5'5" and even with a large frame I'm supposed to be 140 and that's the heavy end. If i weighed 140, I wouldn't look good at all. And it's not just muscle that's not accounted for, there are women who are large breasted as well.

Nakauchi Betty
Nakauchi Betty 5pts

thats true its nener accurate ba how do u know this?????

Marti Bazterika
Marti Bazterika 5pts

Could you use a Man silhouette from time to time?? Thanks!

Lenore Benzi
Lenore Benzi 5pts

Having large boobs can keep a woman from ever falling into the "normal" range.

Ayurveda 5pts

Great! LaOficial Reyes :)

Janine DaPaah
Janine DaPaah 5pts

Tammy, maybe you can take this to your company. :)

Ayurveda 5pts

You'refine! :) healthy keep working towards maintaining it! :)

Becka Hall
Becka Hall 5pts

Thanks for sharing! In short, I certainly don't think it's a sure-way method to tell if you're overweight. Toned/muscly people will measure obese on the scale, however they only have a small percentage of fat.. Therefore to say they're obese can't be correct.

Ashani Fernando
Ashani Fernando 5pts

I got bmi 23 dt means normal ..du I need to more workout to get healthy

Ashani Fernando
Ashani Fernando 5pts

My bmi got 23 dt mean normal ..is dt healthy o need more workout

Ayurveda 5pts

Rouseyy Letty Perez It's alright happens nothing to worry! You look great! :)

Rouseyy Letty Perez
Rouseyy Letty Perez 5pts

Thank you for your reply Ayurveda but i weigh myself every morning like on sunday i was 113 and today im almost 115... lol i get confused... \U0001f602

Ayurveda 5pts

Rouseyy Letty Perez There might be a lot reasons why your weight is varying! It could be because of bloating or after eating a heavy meal you tend to weigh a few pounds extra! Do not worry! :)

Rouseyy Letty Perez
Rouseyy Letty Perez 5pts

I'm at a healthy weight... im around 113 but keep jumping to 115 then down to 113.. it's kind of hard to tell what's my exact weight

Ayurveda 5pts

Dolores Bermudez You're always welcome! :)