Calculating the correct body weight is not a complicated process, nowadays there are many online calculators that make this task easier for us. However, it is important that we know how to properly read the data obtained and that we use the right tool. We’ll give you a hint on how to calculate BMI and show you how it should be formed correctly and what a too high or low result can indicate. We will also look at whether this indicator is authoritative in every case.
What is BMI?
To begin with, it is useful to become familiar with the term itself. BMI (Body Mass Index) is also called the Quetelet index, the second term coming from its creator, Adolf Quetelet, a Belgian statistician who developed the body mass index in 1832. In the most general sense, the BMI index is used to indicate whether a person’s weight is correct, it allows one to calculate body fat content, based on the proportion of body weight and height. Moreover, thanks to this index, it is possible to quickly verify whether our lifestyle and diet are correct, as large irregularities may indicate that we should consider seeking the help of a nutritionist or doctor.
There are many calculators into which you can enter 3 key data yourself – weight, height and gender. In carrying out this measurement, no knowledge of medical examinations is required, all that is needed is the appropriate measurements, which can be easily and seamlessly taken at home, all you need is a scale and a suitable centimeter. After entering the data, we get the result (number), which should be checked in the appropriate range of values. The traditional formula for calculating body weight presents as follows:
BMI = body weight (kg): height (m)2
By weighing and measuring correctly, you can calculate the index, either “on a piece of paper” or using an online calculator. For example, a person weighing 55 kg with a height of 160 cm should divide 55 by 1.6 squared, i.e. 2.56. We will get the action 55: 2.56 = 21.48, which shows that the BMI of such a person is 21.48.
Note that this formula is not always authoritative (the index will not work for children). Nowadays, many online calculators also take gender into account, so in order to get a more reliable result, it is worth using this solution. Gender information is important for biological reasons – the correct fat content for women is higher than for men.
BMI value ranges
An index that is too high or too low can cause various diseases, including obesity, overweight or underweight. When calculating BMI, check the result in the table below:
less than 16 – starvation,
16 to 16.99 – emaciation,
17 to 18.49 – underweight,
from 18.5 to 24.99 – normal value,
25 to 25.99 – overweight,
30 to 34.99 – obese and degree,
35 to 39.99 – obesity of the second degree,
above 40 – extreme obesity.
The normal value is in the range from 18.5 to 24.99, with research suggesting that a slightly higher score does not adversely affect health. However, if a result other than normal is obtained, medical advice should be sought for more accurate information.
Abnormal BMI and prevention
A slightly abnormal BMI is not necessarily a worrying sign, however, a value above 30 should prompt consultation with a doctor or nutritionist. Increased fat mass can cause such diseases as:
ischemic heart disease,
Early diagnosis of such diseases allows faster implementation of individual treatment. Of course, also do not underestimate an underweight BMI (below 17). Possible causes of underweight are:
parasitic or infectious diseases
A situation qualified as critical starvation is a score below 16.
Help in calculating BMI – WHR ratio.
The BMI calculator can help calculate normal body weight, however, the above-mentioned situations and elements have proven that the method is not flawless. The overall assessment can be supported by additional indicators that we can perform on our own at home or go to the doctor, since these tests (unlike BMI) mostly use matched methods and devices.
A parameter that will present us with a lot of information about our health is the WHR (Waist-Hip Ratio). It calculates the ratio of waist circumference to hip circumference. Obesity in women and men is customary in different parts of the body, which is also related to the exposure of different organs to disease. In the case of women, fat is most often accumulated in the thighs and buttocks (gluteal obesity) in the case of men, it is most often around the internal organs (abdominal obesity). It follows that women with a significantly elevated BMI may be less likely to suffer from diseases related to internal organs than men.
Another parameter that can help determine the correct body weight or allow you to achieve your dream figure faster is the CPM (total metabolism) index, with which you can determine the daily kcal requirements of your body, taking into account your lifestyle.
Of course, there are many calculators with which you can calculate these parameters (WHR, CPM or others) nevertheless, each person should be treated individually. When calculating this and other indicators, one should not suggest generally accepted norms, and should go to a specialist for reliable results.
Is BMI a reliable indicator?
Yes and no, we can certainly use it to easily check basic information about our body. However, it is important to remember that BMI is for risk assessment and is a statistical method. In order to obtain reliable information, a number of tests should be conducted to obtain detailed data about our health. However, with the help of the BMI calculator, we can check at any time whether we have the correct body weight and react early if we notice abnormalities or too rapid changes.
The influence of age and normal body weight
As we age, the body begins to change; in the case of the elderly, heavier muscle mass and bone mass decrease, while the amount of body fat increases. Therefore, the calculated BMI of an elderly person may present a theoretically correct result (better than in reality), nevertheless it will be misinterpreted due to the aging process. Moreover, the index does not take into account the fact that, among other things, bone density decreases with age. Older people may suffer from osteoporosis, which significantly underestimates body weight.
Calculated BMI in children – does it work?
Calculators are designed only to calculate the normal body weight of adults (over 18 years of age). For children or adolescents, centile grids are used to see if their development is adequate. In theory, the calculation of the index values is similar, although in the case of children or adolescents, other criteria are taken into account.
Girls at puberty tend to have more body fat than boys – this is also associated with faster development. Among other things, this is why the issue of calculating BMI in children and adolescents looks a bit different, since the traditional (developed by Adolf Quetelet) formula does not take age and gender into account. The calculations themselves look the same, but in this case the obtained result is applied to the centile grid. This action allows you to compare the obtained value with other people of the same sex at the same age.
Norms of BMI in children and adolescents are as follows:
less than 5 percentiles – underweight,
From 5 to 20 percentiles – thinness,
From 25 to 85 percentiles – normal weight,
85 to 95 percentiles – overweight,
above 95 percentiles – obesity.
It should be borne in mind that the result obtained is most often used for statistics. Assessment of the health of adolescents and children in the context of body weight should also take into account other parameters and the continuous changes that occur in the “growing body.”
Muscle and bone mass impact on BMI value
People who train in sports may often wonder whether the ranges of values for normal BMI make sense for them. Muscle is dense and much heavier than fat. This causes two people of the same weight and height but with different lifestyles to look very different. This is related to the ratio of muscle to fat mass. The BMI index does not take these issues into account in the calculation, resulting in people who regularly or professionally participate in sports are often classified as overweight or obese, which theoretically translates into an increased risk of various diseases. In reality, sports people with a BMI indicative of obesity are not at risk for diseases attributed to that weight, as it is not due to excess body fat.
Another element that affects weight is bone mass (degree of mineralization and density). It is possible to distinguish between people with a petite physique and so-called thick-boned people, in which case people of the same height and weight can also look quite different.