Calculation of BMI and difference with the IMG

Have you ever wondered what your ideal weight is? Then you must have come across one of the many articles answering the question: How to calculate BMI or BMI? What we call BMI is the body mass index. It is often part of the arsenal of slimming tools.

But you will see that not everyone considers this index as a reference. Why not?

Because today, some people say that it is not useful, that it is not reliable, but that it is necessary to calculate the Fat Mass Index (not very appetizing). Some specialists will tell you that you should talk about BMI and not BMI.

The real question is: “So, what should be calculated: BMI or IMG?”

That's what this article will try to explain to you. In any case, it will help you to simplify all this in your heads to take advantage of it.

But first, here are the different aids and calculators that can be found on the blog about this subject...

Articles and free calculators on this site

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How to calculate BMI?

For those who have not been following closely, the body mass index is supposed to tell you how much you should weigh to be healthy. It's a sort of ideal weight calculation or fitness weight as we often say. To calculate your BMI, you simply need to know 2 benchmarks: weight and height. That's all you need to know.

Take the example of a man who is 1.76 m tall and weighs 72 kg. I will spare you the mathematical formula for calculating this body index, since everything is on the table below: 

BMI calculation with a table according to weight, height and age

A BMI calculator to go faster

Even if you are not a mathematician and you don't have a BMI calculator, just look for her body mass index on this chart. You will find 22 (in the green = normal BMI). This means that this person is of normal build, that he is keeping his weight down. Great for him!

If he had weighed 96 kg, he would have been in the “moderate obesity” boxes.

Use this table if you want, but you will understand as you read on that this system has a number of problems. 

If you want to know everything without paying anything, you should know that my BMI is 24 and that I am in the light green (just). All you have to do is look up my height and weight. You will find that I am between 1.46 m and 2.10 m tall, and that I weigh between 42 and 108 kilos. If you are good private detectives, you should be able to find the clues all over the blog. Good luck!

Come on, on this interlude as silly as it is useless, I invite you to move on, because we don't have that much to do anyway...

Limits of BMI calculation because of Arnold

I'm not sure I need to introduce you Arnold Schwarzenegger (what a rotten name anyway…). He was named Mr Olympia 7 times. When he was at his peak, he weighed 106 kg for 1.88 m during competitions, and about 120 kg out of competition. 

If you take the painting again and look at the photo, it means that it is borderline moderate obesity during competitions… and not far from severe obesity out of competition. Finally, it's not so bad to be obese... 

Out of curiosity, I visited the site and I entered Arnold's information. Here is the result :

According to the classification of the WHO (World Health Organization), the interpretation of your BMI (29.99 kg/m²) is: Overweight

Our recommendation for your overweight: You are overweight and your BMI is over 28, which means you have reached the stage where the death rate is increasing. You are close to the stage of obesity. Weight loss can be considered, avoiding private diets (harmful to health), we advise you to take a look at our newsletter! 

From time to time, you will receive useful and interesting information on good recipes, nutrition, body build, etc.

Poor Arnold… And yet he had a thin waist. Maybe not even enough visceral fat, because enough is needed to protect internal organs.

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And if you pass the weight and height of the last winners of the Mr Olympia competitions in a BMI calculator, it is much worse, since they will be classified in the morbidly obese category. 

Well, at the same time, it's so naughty, bodybuilders 🙁 Finally, it's only my opinion… You think I'm jealous, no doubt!


Should you calculate your BMI or throw it away?

Of course, this example is an extreme case. But it easily shows you the limit of this calculation which does not take into account the muscle mass nor the true percentage of fat mass. On closer inspection, it seems that this formula is quite a good indicator of thinness or anorexia problems, but not necessarily overweight or overweight.

Indeed, if you are relatively muscular, even without reaching the level of Mr. Olympia and without even being part of the high level athletes, you will easily find yourself classified as overweight. This is why Wikipedia reminds us that this formula is only an indicatorand not an absolute figure of normal weight.

So you have to be very careful in interpreting the results and not tell yourself “Ah, here is my ideal weight, I have to lose weight quickly to reach it”.

The online encyclopedia also explains that some athletes have a body mass index above average without incurring any danger. In addition, the BMI should be calculated according to the measurements, morphology, build or musculature.

A stocky person will not get the same results as a lanky person. And that does not mean that the first must go for a spa treatment, undergo medical monitoring, consult a dietician or follow any diet. No, not so fast!

This brings us to another method of calculation.

The fat mass index or IMG calculation

This is what we have been hearing about for the past few years. In short, it's simply the amount of fat in your body compared to everything else.

For those who don't understand quickly, the rest is the organs, bones, tendons, muscles, etc. That's all you don't want eliminate to lose weight 😉 Between BMI or IMG, there is therefore a big difference in the method of calculation.

The advantage of body fat index over body mass is that it focuses on what you are really interested in: the fat rate. And what is remarkable is that the body weight of 2 people of the same size can turn out to be different with the same fat rate.

What is the right percentage of fat in the body?

That's a good question. Here is a table showing generally accepted body fat levels:

Essential grease10 to 13 %2 to 5 %
Athlete14 to 20 %6 to 13 %
Fitness21 to 24 %14 to 17 %
Acceptable25 to 31 %18 to 24 %
Overweightover 32 %over 25 %

The first line says “essential grease“, because in reality fat is essential for our survival and our physical form. The 0 % of fat is only for yogurt 😉 But I'm sure you're not a yogurt. Or you are the first to read one of my articles. And there, I say congratulations!

Among other things, fat is used to protect internal organs and as an energy reserve. In fact, you can get about 7000 calories from one kilogram of fat.

That's why bodybuilders don't stay at their competitive level all year round. Not only would it be dangerous, but they couldn't even train.

Silhouette program

Some methods to calculate your Fat Mass Index

There are a handful of more or less effective and more or less expensive self-measurement methods to achieve this.

For example, you can find quite original methods like the "calculation of the fat mass index with the size of the wrist" (or its circumference rather). The name doesn't make you dream, that's for sure, but the method seems to be quite efficient and doesn't cost anything.

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Another method is to purchase an adipometer to measure subcutaneous fat. This instrument of torture is also called "skinfold forceps", like the one you see just below.

The advantage of these little measuring tools is that they cost a pittance and are still reliable enough to calculate your IMG. Plus, you can use them at will. Others use an impedance meter.

The operation of this type of scale relies primarily on the amount of water in your body and its resistance to electric current. Your level of hydration therefore inevitably has an impact on their calculation. However, they have the merit of existing, of being easy to use to determine your healthy weight and quite cheap.

[BAND METER AND SEWING METER] - Skin fold pliers and...
[PRO SPI GAUGE AND SEWING METER] - PRO skin fold pliers and...
RENPHO Impedance Meter Scales Connected Balance...
Withings Body - WIFI Connected Scale with Weight and Body Monitoring...
[BAND METER AND SEWING METER] - Skin fold pliers and...
[PRO SPI GAUGE AND SEWING METER] - PRO skin fold pliers and...
RENPHO Impedance Meter Scales Connected Balance...
Withings Body - WIFI Connected Scale with Weight and Body Monitoring...
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Current price
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29,95 €
40,99 €
59,99 €
[BAND METER AND SEWING METER] - Skin fold pliers and...
[BAND METER AND SEWING METER] - Skin fold pliers and...
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Current price
9,99 €
Click for more information
[PRO SPI GAUGE AND SEWING METER] - PRO skin fold pliers and...
[PRO SPI GAUGE AND SEWING METER] - PRO skin fold pliers and...
Our rating
Current price
29,95 €
Click for more information
RENPHO Impedance Meter Scales Connected Balance...
RENPHO Impedance Meter Scales Connected Balance...
Our rating
Current price
40,99 €
Click for more information
Withings Body - WIFI Connected Scale with Weight and Body Monitoring...
Withings Body - WIFI Connected Scale with Weight and Body Monitoring...
Our rating
Current price
59,99 €
Click for more information

Techniques more laborious than body mass index

I won't dwell on that because it is of little interest to us. But be aware that there are other scientific methods if you want to know your body fat index with precision such as this one:

  • The dual-energy X-ray absorptiometry scanner. It must be sponsored by Luke Skywalker or Master Yoda…
  • Hydrostatic weighing based on Archimedes' principle. You know, any body submerged in liquid is considered lost if it hasn't come to the surface within an hour (or something like that) 🙂
  • Body Densitometry. This technique calculates your body fat based on air movement. It measures your body mass, volume and body density.

These methods are effective, but the prices for benefiting from them will set you back. It's up to you. To learn more, read this article.

Anyway, I'm now going to show you that everything I explained to you is useless, or almost... 

Because pictures speak louder than words

How to calculate your IMG quickly? Well, the easiest and fastest is the judgment of your eye. You can tell right away if you are too fat or too skinny.

By looking at photos of people whose fat mass index is already calculated, it is very easy to situate yourself. Nope ?

BMI or IMG calculation for men and women
Prefer visualization of fat mass

Now you just have to stand in front of a mirror to compare. You will immediately have a pretty good idea your fat level.

Beware of bad faith! Don't say "I'm at 10 %" if you look like the photo on the right. You can also use this kind of photos to determine what your goal is and gradually determine what your ideal weight is.

This leads directly to the next question...

Why calculate your IMG?

Let's face it, knowing your fat level is especially important for your health. Indeed, it is now obvious that overweight people put themselves in great danger. Among the risks associated with an excess of adipose tissue are certain diseases such as:

  • sleep apnea
  • cardiovascular illnesses
  • stroke
  • high blood pressure
  • high cholesterol (LDL)

We could also add to the list all the consequences on the overstressed joints.

People who are very fat must therefore review their eating habits and rebalance in order to lose a few pounds quickly. If you are in this case, don't waste time!

Learn to eat a balanced and healthy diet. Evaluate your caloric needs to create a deficit. Your dietary balance may even go through a new distribution of macronutrients.

ALSO READ:  3 steps and 10 tips to lose weight

I know this all sounds painful, but limiting your calories per day is essential to winning and keeping the line. Remember that it takes 7000 calories burned to get rid of one kilo of fat.

This is why I have developed a simple and effective method to learn how to have a balanced diet, but also how to lose fat, lose weight and keep your ideal weight for life without suffering:

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Set your body fat goal

Frankly, if you just want to look fit and healthy, the level “Fitness” is more than enough. That is to say 14 to 15 % for men and 20 to 21 % for women (3rd photos from the right).

If you compete and want the best athletic performance level, you will have to go down to 15 % for a man and 20 % for a woman.

Do you want to have really visible abs? A 6-pack or chocolate bars? So there, you will have to lower your fat level to around 10 % for a man and 15 to 17 % for a woman. It is not so easy. Especially after 40 years (Ouch, it hurts).

And I warn you: you often have to change your lifestyle and follow a low-calorie diet to get there. And the hardest thing is to maintain your ideal weight all year round, especially at the end of December… Go figure out why!

Know that the best you can keep throughout the year is a level "Athlete". Below, you need a morale and a will out of the ordinary. Sometimes even a good doctor… and some products from his back room, if you know what I mean. But none of that with us, huh Lance Armstrong?

After that, if you just want your friends to say "Hey, you look great! you can be happy with 18 % for a man and 20 to 23 % for a woman.

A little extra note

I would like to point out that the Body Fat Index, as its name indicates, is only used to determine the quantity of fat in the body. It obviously has nothing to do with your muscle volume.

Which means that 2 people can have exactly the same IMG rate and be totally different. Here is an example with 2 men at 10 % of IMG:

Different percentage of muscle mass
Different male BMI – different muscle mass percentage

Do you see the difference ? Or, go immediately to buy glasses, a white cane and a Labrador 😉

IMC or IMG: What are you going to do with it?

Now that you're a pro at calculating BMI or BMI, you understand that the most important thing is the reflection in your mirror. Mirror, oh my mirror, tell me who is the most beautiful (or the most handsome) in the Kingdom? 

Look at yourself and ask yourself the question: “Do I want to change anything about my appearance?” 

NOPE ? It's great for you! Next…

YES ? Do you want to gain muscle, lose fat or both? Then start by applying the tips you read on this blog week after week.

Put into practice!

Yes, apply what you read and forget about your ideal BMI. Move, sweat, watch what you eat without depriving yourself. Determine your calorie needs if that motivates you and track your progress month by month.

Your primary focus should not be your aesthetics. Indeed, the fat mass index has a direct link with your state of health and many pathologies such as heart disease and blood pressure. Never forget it.

That concludes our lesson today on calculating your Body Fat Index and ideal body mass. I hope you see it a little clearer, because I won't do that every day...

Tell me what you think by leaving a comment below. Thanks in advance!

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2 réflexions sur “Calcul de l’IMC et différence avec l’IMG”

  1. Hi,

    I'm preparing for an ultra marathon, I'm starting now so I'm starting from zero (hey yeah: p) Well, I have a physical job, it helps anyway.

    According to what you write I am moderately obese, well that seems a bit exaggerated to me but let's admit, I'm not all skinny but still :p

    To make ultra teak, you advise to target which IMG? Because frankly fat is going to be needed to hold on anyway, even if marathon runners are generally quite skinny.

    I might ask you 2 3 little questions 😉 I did a lot of sport, but that was before!

    I would point out that I'm not doing this to lose weight, I don't care a bit about that, it's mainly for the form, the heart, and the challenge. And especially because it is in one of the most beautiful places in the world.


    Mr Puffin

    1. When you say ultra marathon, I assume you are referring to a 50-100 km run or walk. If you talk about moderate obesity, I think you are referring to the BMI calculation which is not the most effective, especially if you already have a little muscle volume. This is probably the case if you have a physical job 😉

      So you're not fat, and the photos in the article will help you really gauge your fat level. Afterwards, if you don't care, it doesn't matter as long as you have the physical condition.

      But on an endurance event, you can't place yourself too high in IMG because the heavier you are, the more effort you will need to reach the end. It seems to me that the ideal for having endurance and an acceptable weight for the effort is in the fitness category (this is my profile at over 48 years old). Which means that at best, you will see your first 2 rows of abs. Even if you can't see your abs, you need to at least have a flat stomach. This means an IMG between 14 and 17 %. Otherwise you will be too heavy.

      So even if you're not doing this to lose weight, I think you have to stick to it a bit. The quickest way is to increase your protein intake to 2 g per kilo of body weight per day and reduce your intake of slow and fast sugars until the event. So eat more meat, fish, eggs… accompanied by colored vegetables and less pasta, rice, etc. (and only wholemeal). You'll see, it's magic.

      Good luck and congratulations on your lovely blog!

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