How to calculate your BMI easily (free calculator)

Of course, the BMI is far from being a perfect index as you will see by reading the rest of this page. But it has the merit of existing and of providing a global standard applicable to most individuals.

It is a useful indicator above all for adult men and women who want to change their habits. You will see that it is a motivating factor for resuming regular physical activity or correcting eating habits.

Free BMI Calculator

It's very simple, you just have to fill in the 4 information in the BMI calculation table below. The results are based on the recommendations of the World Health Organization (WHO).

Note that this calculator is advanced enough to include weighting according to age, which is not systematic in the calculation of BMI.

Calculate your BMI

Fill in the 4 dots and click the blue button

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How to calculate your BMI?

I will try to give you some important pointers here. And since this is not the only interesting clue, I explained in another article the difference between BMI and IMG (Fat Mass Index).

What is BMI?

We can define the Body Mass Index as am according to the site MedicineNet (in English): A key index for relating weight to height. It is calculated by dividing the body weight in kilograms (kg) by the square of the height in meters.

The formula is therefore this for someone who weighs 78 kg and is 1.80 m tall: BMI = 78 / (1.80)² = 24.07

The results can be compared to this BMI table:

How to calculate your BMI with a table

To make it a little more readable, I offer this summary:

BMI (kg/m2)Interpretation (according to WHO)
Less than 16Anorexia or malnutrition
Between 16.5 and 18.5thinness
Between 18.5 and 25Normal build
Between 25 and 30Overweight
Between 30 and 35Situation of moderate obesity (Class 1)
Between 35 and 40High obesity (Class 2)
Over 40Morbid or massive obesity

Not perfect, but world famous

The main disadvantage of this formula is that a very muscular or large-boned person could have a high BMI without this increasing their health risks.

However, the World Health Organization (WHO for friends) has been using this index since 1997 to establish a reference standard classification in terms of overweight. So, even if the BMI does not only have advantages, it has the merit of being able to be used all over the world.

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As you will read in the FAQ part at the end of the article, each BMI threshold should be different between a man and a woman. This system would thus gain a little in precision.


Why calculate your BMI?

One could indeed wonder why use it if it is not reliable at 100 %. Well already because it is valid for most people of the planet, which is not bad. You do not believe ? It is used for women and men. Normally it is not suitable to be used for children or teenagers because their growth is not complete.

For a doctor who needs to determine if a person is overweight or underweight, this is a really handy and quick shortcut. He can note that quickly in your health book. And for a non-professional like you and me, it's all the more useful.

In some cases of observed morbid obesity, this may lead the doctor to consider treatments or an operation to bariatric surgery. This consists, as in the case of the installation of a gastric band, in modifying the anatomical structure of the stomach and the intestine to reduce the daily calorie intake.

The objective is then to return as quickly as possible to a reasonable body weight in order to avoid complications. However, it is necessary to take into account the possible risks associated with such an operation…

Body Mass Index: Advantages and Disadvantages

So remember these benefits:

  • great ease of calculation since you only need to know your weight and height and run it through a simple formula (see above);
  • An indicator used worldwide, thus making it possible to make statistics on a global scale.

But this ease of calculation as well as this international generalization reveal the following drawbacks:

  • The silhouette or the size are not taken into account. This is why bodybuilders are almost always considered obese in these charts even though they have thin waists;
  • Basically, determining factors such as gender, age or even ethnic origin are not taken into account. Developments have, however, made it possible to integrate a weighting taking account of age.

These drawbacks can therefore distort the results obtained. It is therefore important to remain objective in the analysis of the BMI calculation. Now if you don't mind being classified as morbidly obese like Arnold Schwarzenegger, no problem 😉

It is true that at this level, fat mass index, or IMG, is much more reliable for knowing if you have a balanced diet or if you are overweight. But it is also much more complex to determine. You will still find a tool on this site to achieve this.

Calculate your BMI for motivation

How to calculate your BMI to motivate yourself

In reality, calculating a person's ideal BMI is a easy first step to motivate yourself if your weight is too high or you have too much abdominal fat. It is often one of the first slimming tools that specialists use to assess whether the patient is in good health based on their personal data.

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And finding the motivation is essential to regain a normal corpulence, and therefore an acceptable state of health. Keep in mind that excess visceral fat is important cause cardiovascular disease or type 2 diabetes, and therefore early mortality. This is, for example, what this study on the cardiovascular risk factor.

When you calculate your index, it's as if you're sending yourself a message like “Come on, I'm going to lose weight or get rid of this fatty mass that bothers me for any physical activity”. This is essential if you have to follow a somewhat strict diet due to significant excess weight or even severe obesity.

The calculation of one's BMI is, in a way, the starting point of the journey towards your ideal weight. After all, you have to start somewhere when you have a weight loss goal and want a better life expectancy.

Silhouette program

Calculate your index and act!

Whether you are overweight or underweight, your health may be at risk. A healthy lifestyle therefore involves doing everything you can to correct any imbalance if it is within your power.

If you have a BMI higher than the recommendations

Yes, it is of course not enough to sit down to calculate your body mass index without doing anything afterwards. It will not solve your risk of disease or your possible complex due to a larger than normal waist circumference. Also remember that abdominal obesity is the root cause of many cardiovascular diseases.

You need to do something about it if you don't have a normal BMI according to the WHO scale. To regain your healthy weight, you will have the choice of slimming methods and diets. However, I encourage you to do not undertake a low-calorie diet that is difficult to maintain over the long term. It is extremely important to continue to have fun, including when you want to lose weight quickly and reduce your waistline.

However, most people end up giving up when they have to make daily calorie calculations. It can be really annoying...

Afterwards, it is up to you to determine how you will regain a normal weight and gain muscle mass. For my part, I followed this program to lose 15 pounds at the age of 47, without depriving myself and without suffering (while I am a big good eater):

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If you have a lower than normal BMI

It is true that we think more often of overweight people when we talk about BMI. But that would be to forget that people suffer from thinness which complicates them just as much. 

Many studies such as the one revealed on the Radio Canada website indicate that there is a link between being too low in weight and an increased risk of premature death.

It is therefore important to watch your weight, including when you need to grow. You can learn more about this by reading this article to help you gain healthy weight.

Calculate your BMI: Conclusion

As you will have understood, this index is not reliable at 100 %, but it has the merit of providing a useful reference at first. BMI alone should not be taken as gospel to draw definitive conclusions.

This is only one element of the nutritional assessment which should include a clinical examination and consideration of the context (sport, pregnancy, etc.).

Leave a message in the comments area below to share your experience or ask questions.

FAQ – Answers to your questions

Is a woman's BMI calculated differently?

No, but it should be. In view of the many studies conducted, it therefore seems fair to say that the ideal male BMI should be between approximately 21 and 27, while the calculation of the ideal female BMI must be between 19 and 25. On average, men's BMI thresholds should be 2.3 kg/t2 higher than women's.

Is BMI the best index for overweight?

No, but it's the fastest and most direct. For more precision, it is better to turn to the Fat Mass Index which aims to establish the percentage of fat in your body. The IMG has the advantage of not being distorted by muscle mass and does not depend on age, sex or other important factors.

What does BMI mean?

It is the acronym for “Body Mass Index”. It is an indicator that establishes the relationship between a person's body weight and height. This simple calculation allows you to quickly tell if a person is too thin, at an ideal weight or overweight compared to an established average.

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