How to calculate BMI?

How to calculate BMI?
It takes approx. 3 minutes to read this article

BMI (Body Mass Index) is a coefficient that allows us to calculate whether the proportion of body weight to height is correct. How is it calculated? What are its main advantages and disadvantages?

BMI – what is it?

BMI (Body Mass Index) was developed by Adolf Quetelet – a Belgian statistician. Until the seventies of the twentieth century, this indicator was the only source of knowledge about the correct body weight. Initially, it was used only to measure the body weight of adult men and women. The introduction of the percentile grid enabled BMI to be measured also in children and adolescents. Until recently, BMI has only been used to diagnose obesity, allowing us to predict the possible risk of developing overweight problems. Currently, however, this coefficient is also used for other purposes, such as determining the correct weight. It significantly facilitates the adjustment of diet and physical activity

to individual predispositions.

BMI calculation step by step

How is BMI calculated? It is very simple! Just divide your weight in kilograms by your height in meters squared. With BMI it is possible to determine whether your weight is normal, underweight or overweight. For this purpose, it is necessary to consult the BMI classification in force all over the world. It is presented as follows:

< 16.0 – starvation,
16.0 – 17.0 – lean,
17.0 – 18.5 – underweight,
18.5 – 25.0 – normal weight,
25,0 – 30,0 – overweight,
30,0 – 35,0 – I degree obesity,
35,0 – 40,0 – II degree of obesity,
> 40,0 – III degree of obesity.

BMI of children and adolescents is calculated in the same way with the difference that the result is compared with the average results of peers of the same sex.

Advantages and disadvantages of BMI

What are the main advantages of

BMI? Its undoubted advantage is the ease of calculation. On the web you can find dozens of free calculators that allow its calculation in just a few seconds. BMI provides a lot of valuable information. Properly implemented early preventive measures can eliminate the risk of overweight, obesity, atherosclerosis, or type 2 diabetes. BMI is applicable to any person, regardless of age and gender.

This coefficient is not without its disadvantages, of course. One of them is its inaccuracy. For some patients, it may give a somewhat distorted picture of reality, not reflected in the actual state of health. It works much better for populations than for individuals. It is also worth mentioning that BMI is physiologically inappropriate. It does not take into account factors such as actual body fat, muscle mass or bone density. Sometimes we have to deal with a situation in which a slim person does not have a low BMI at all, which is not related to obesity, but intensive training


The disadvantage of the described coefficient is also that it refers to an ideal group, not taking into account individual predispositions of a person. It should also be noted that BMI is identical for men and women, which precludes obtaining reliable results with its help. Women have a natural tendency to accumulate less muscle mass and more body fat than men. When a man and a woman are of similar height and weight, their BMI will be similar. However, a man will have a smaller proportion of body fat. Body fat percentage significantly increases the risk of various diseases directly related to obesity. Knowing only a person’s height and weight, there is no clear way to determine what the correct body mass should be.

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