The BMI is calculated using the following mathematical formula: BMI = weight / height². How is BMI calculated? The body mass index is calculated by dividing the weight by the height squared. Thus, one must measure these two factors beforehand. For instance, if your height is 1.70 meters, you multiply this value by itself, i.e., 1.70*1.70, resulting in 2.89. Then, for a weight of 63 kg, for example, you would divide this figure by 2.89, yielding a 21.8 kg/m² BMI.

According to the WHO references, the figure corresponds to a specific weight category. Indeed, the World Health Organization has defined this index as the standard for identifying weight issues. It remains a reference value, even though it can be contested based on specific unaccounted criteria.

Through research, thresholds have been established to assess risk areas, particularly for cardiovascular diseases.

BMI is a reliable method for adult men and women between 18 and 65, with the calculation being the same regardless of gender. It can be calculated quarterly or annually to get an idea of the category one belongs to. Indeed, various factors can influence the result: occasional weight gain, metabolism, heredity, pregnancy, and menopause… The key is to stay within a healthy weight range.

However, BMI cannot be used in some instances, notably in pregnant or breastfeeding women, seniors, endurance athletes, or highly muscular individuals. Their muscle mass skews the result in these latter cases, as BMI does not distinguish between muscle mass and fat mass.

For a child or adolescent, the weight curve found in their health record remains the most reliable indicator. However, specific calculators exist to calculate the BMI of children and adolescents, taking into account age and gender specifics.

The interpretation of BMI is made according to the criteria defined by the WHO. Here are the main guidelines. Depending on the obtained figure, each individual falls into a category.