BMI (Body Mass Index): All you need to know about BMI

Body Mass Index

Our daily life brings in a lot of challenges. Gaining excess weight is one of them. The chances of gaining excess weight or being obese are not only due to overconsumption of food or bad eating habits but could arise from numerous factors. Hence, it becomes necessary to keep our body weight or body fat in check and maintain a healthy body. 

It begins with examining or measuring the body weight and the amount of fatness or the body size. And what could give a better measure of body size than a BMI calculator? You must have heard about a BMI calculator but might not know what BMI is. 

A BMI calculator measures the BMI using a body mass index formula. If you have never seen a BMI chart or used a BMI calculator, you might question what BMI is. So let us walk through a discussion on BMI or body mass index and decipher how it could help us.

What is BMI?

BMI stands for Body Mass Index. It is a measure of body size or body fat. Body Mass Index relates the bodyweight of a person to their height and gives a measure of the correctness of body weight according to the height of an individual. 

Body mass index tells you which category of the population you belong to based on your weight and height. The category is divided into an underweight, healthy weight, overweight, and obese. Hence, Body mass index or a BMI calculator can be used as a screening tool to determine if an individual possesses a healthy weight to avoid the risks of diseases caused due to obesity.


Formula to calculate body mass index

Now that it is clear to you what BMI is, you might wonder how a BMI calculator works and what is the body mass index formula. As mentioned earlier, body mass index uses the weight and height of an individual to give a measure of body fat.

You can either use an online BMI calculator or the body mass index formula to determine the degree of fatness of the body. You can measure body mass index in the metric or imperial systems using the body mass index formula or a BMI calculator. 

The body mass index results are compared with the ranges on a BMI chart, and the category of body weight is determined. The formula to calculate the Body mass index is the same for adults and children. However, the ranges on a BMI chart differ, and the BMI chart is used differently for adults, teens, and children, as we shall discuss later. 

Here is the formula to calculate Body mass index, which gives similar results to a BMI calculator.

  1. Weight in kgs and height in m

It is the metric system of measurement of the body mass index where the body weight is taken in kilograms, and the height is taken in meters. We usually measure height in centimeters. So you must divide it by 100 to convert it into meters.

Formula= weight (kg)/ [ height (m) ]2

2. Weight in pounds and height in inches

It is the imperial system of measurement of body mass index. The body weight is taken in pounds (lbs), and the height is taken in inches. Here we multiply the body mass index by a conversion factor of 703 to get results from a BMI chart.

Formula= [ weight (lb)/ [ height (in) ]2 ] * 703

Hence, now you can determine the body mass index using the given formulas using the units you prefer and compare your results with a BMI chart. Now you know much more than what BMI is. 

The need to undergo a BMI test

We have been discussing what BMI is and how to use a BMI calculator until now. However, you might wonder what the need to undergo a BMI test or use a BMI calculator is. Through our discussion on what BMI is, you must have understood that body mass index gives a measure of body fatness, which is an essential factor to know in daily life.

The need to maintain a healthy body weight to avoid the consequences of obesity, malnutrition and the diseases associated with them arises the need to measure the body mass index. You must know what the definition of obesity and malnutrition is. While a low body weight or low BMI can lead to numerous diseases and increase the risk of malnutrition, anemia, osteoporosis, etc., high body weight or high BMI indicates a risk of obesity.

Obesity usually leads to numerous lifestyle diseases, such as high blood pressure or hypertension, type 2 diabetes, coronary heart disease, stroke, high LDL cholesterol, low HDL cholesterol, high levels of triglycerides or dyslipidemia, gall bladder disease, sleep apnea, breathing problems, osteoarthritis arising from the breakdown of cartilage and bone within a joint, increased oxidative stress, chronic inflammation, etc.

Obesity might also lead to several cancers in the body, such as breast, colon, kidney, liver, gall bladder, endometrial, etc. People with obesity also suffer from mental illnesses such as anxiety, mental disorders, clinical depression, stress, etc. They also experience frequent body pain and improper physical functioning of the body. Eventually, obesity leads to low quality of life and even mortality.

Hence, to keep yourself away from obesity and its lethal consequences, it is necessary to keep track of the body mass index. So you must use a BMI calculator regularly and examine your body fatness based on the body mass index chart. 

Why is the body mass index a popular measurement for fatness?

Body mass index is a popular tool to measure body fat, and even doctors use a BMI calculator to determine the appropriate body weight of populations. The reason behind it is that Body mass index is an inexpensive, simple, and easy screening tool to measure body size.

Now that you know what BMI is, you must be able to decipher that though it is not a direct measure of body fat, Body mass index correlates with the direct measures of body fat. The best part about using body mass index as a measure of body fatness is that it uses only weight and height and a simple formula to give the body mass index of an individual.

You can also use units of your choice, either in the metric system or imperial system. You can use the body weight in kgs and height in meters in the metric system. You can use bodyweight in pounds and height in inches in the imperial system. Hence, calculating BMI is as simple as defining what BMI is, and you can determine if you are obese or overweight in a matter of seconds.

Can BMI give a complete diagnosis of body fatness?

Through our studies related to what BMI is, it is clear that body mass index is a measure of body fatness. However, it is not a direct measure of body fat and does not give a complete diagnosis of an individual's body fatness or health.

Hence, medical practitioners usually combine body mass index measurement with other measures of body fat to determine body fatness. Some assessments in addition to body mass index might include diet evaluation, skinfold thickness measurement, the amount of physical activity performed by the individual, and family history. 

Hence, BMI can give a complete diagnosis of body fatness only when combined with results from other body fat assessments. You can measure your BMI using a BMI calculator and consult your physician for further evaluations.

Can you rely on BMI as a measure of body fatness?

Now that you are well aware of what BMI is, you might question if you can rely on body mass index as a measure of body fatness. Through several studies on BMI and the interpretation of the results obtained through a BMI calculator, the scientists have found a high correlation between body fatness and body mass index.

The accuracy of body fatness according to the body mass index also differs from an individual's body mass index score. An individual with a high body mass index or high amount of body fat has a greater chance of getting an accurate Body mass index using the body mass index formula or a BMI calculator.

The body mass index chart for adults

In order to determine the category of body weight an individual belongs to, they must compare the results obtained from a BMI calculator to the values on a BMI chart. So if you know what BMI is, you must understand that a low body mass index indicates a healthy weight, and a high body mass index indicates obesity. 

Here is the BMI chart used to measure the degree of fatness in adults. The body mass index in the case of adults, that is, 20 years old and older, is interpreted using standard weight status categories. It is the same for men and women belonging to all body types and ages.


Weight category


Weight category

Below 18.5



Healthy weight



30.0 and above




Hence, now that you know what BMI is and how to use a BMI chart, you can determine the appropriate body weight according to your height to fall into the healthy weight category of the BMI chart. 

How is BMI calculation different in the case of children and teens?

As stated above in the BMI chart, body mass index is used only for adults. The Body mass index interpretation differs in the case of children and teens even though the body mass index formula and the BMI calculator are the same for all.

In the case of children and teens, the Body mass index also relies on sex and age. It is because the amount of body fat changes with the age of children and teens, and it also differs between boys and girls. Hence, the BMI percentile is considered in the case of children and teens rather than the Body mass index score directly.

You can refer to body mass index charts for different age groups and determine the appropriate body weight depending on your children's height, age, and sex so that they fall in the healthy weight category of a Body mass index percentile chart or graph.

How does BMI differ in athletes?

The body mass index of people belonging to the general population and the athletes differ. Even individuals' body mass index from each category may be the same, but it indicated different results regarding body fatness. 

Through our studies on what BMI is, you only know that body mass index measures body fatness, and a high BMI indicates obesity. However, a high BMI in the case of athletes might be due to increased muscularity, and it does not solely indicate a high amount of body fat.


Through the overall discussion on what BMI is and its aspects, we can conclude the importance of a BMI calculator and the need to measure BMI to reduce the risks of diseases associated with obesity. Hence, get a BMI calculator and determine if you belong to the healthy weight category. Also read How Many Daily Calories Should You Eat Per Day to Lose Weight

Authored By : Poorvi Chhajer

About Author : Poorvi is a psychology graduate with a knack for writing and belief in ayurveda.

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