Calculation of the Body Mass Index

The ‘ Body Mass Index (or BMI, Body Mass Index for whoever knows the English) is a biometric parameter defined for the first time since the Belgian mathematician and statistician Adolphe Quetelet (is also called the Quetelet Index) in 1835.

L’ BMI does not measure an individual’s body fat percentage, but provides data that can estimate a person’s health status in relation to their body weight.

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More precisely, the body mass index relates the height and weight of a subject, through the formula

BMI = kg / m 2

where “kg” are the kilograms of weight of the subject and “m 2 “ is the square of his height expressed in meters.
Let’s take a practical example for a subject weighing 65 kilograms and 1 meter and 70 centimeters tall. The formula is:

BMI = 65 / (1.70) 2 = 22.49

We evaluate the number based on the tables drawn up by the World Health Organization (WHO or WHO, again for English speakers), which divide the population into 4 different groups:

AssessmentBMI (kg / m 2 )
 Main intervals
Additional intervals
Severe thinness<16.00<16.00
Moderate thinness16.00 – 16.9916.00 – 16.99
Mild thinness17.00 – 18.4917.00 – 18.49
Normal weight
18.50 – 24.9918.50 – 22.99
23.00 – 24.99
Pre-obesity25.00 – 29.9925.00 – 27.49
27.50 – 29.99
Class I obesity30.00 – 34.9930.00 – 32.49
32.50 – 34.99
Class II obesity35.00 – 39.9935.00 – 37.49
37.50 – 39.99
Class III obesity≥40.00≥40.00

Clearly, in order to consider the BMI as a relevant data, it is necessary that the subject in question has a body composition within the norm.

 If we take a bodybuilder, for example, his BMI will certainly be high, despite having a percentage of fat mass below the average of the population.

A further criticism of the evaluation system proposed by the WHO is the lack of distinction between men and women, who are thinner, so they should be able to have a separate table.

However, in the absence of more accurate systems to evaluate the percentage of a fat mass of a subject, the use of the BMI is a good starting point. For this reason, we propose below an automatic system to calculate yours.

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