BMI Formula: How the Body Mass Index Is Calculated

The body mass index is a simple tool that quickly gives you an orientation about your own weight in relation to your height.

The BMI was developed in the early 19th century by the Belgian statistician Adolphe Quetelet to calculate general averages for population groups.

All you need to do is enter your height, body weight, and sex into the BMI calculator or the BMI formula and you will find out whether you are underweight, normal weight, or overweight. This way, you can also find out what your ideal weight is.

The BMI is used by the World Health Organization ( WHO ) as a measure of a healthy body weight. The German Nutrition Society and the Austrian Nutrition Society support this.

BMI Calculator – quick and easy calculation of BMI

Here you can calculate your BMI value quickly and easily. All you need to do is enter your gender, weight and height and the calculator will work out your BMI.

Calculate your BMI now!

BMI formula – What does the BMI value indicate?

The BMI – Body Mass Index – is a rough guide for assessing body weight in relation to height. You can use the BMI to quickly and easily check whether you have a healthy weight.

How do you calculate the body mass index (BMI for short) using the calculator?

The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m ²). For example, the formula for a woman who is 1.60 m tall and weighs 52 kg gives a BMI value of 20.3. This indicates that the woman is of normal weight.

Which BMI values play a role?

The most important BMI values (according to the World Health Organization – WHO) are 17.5 to 24 for women and 18.5 to 24 for men, as these mark the range of normal weight. More details can be found at BMI women and BMI men.

What do the BMI and the individual weight classes indicate?

BMI formula – underweight

Being underweight can have many causes:

• stress
• a lot of exercise
• chronic illnesses – especially in the gastrointestinal tract and metabolic disorders
• malnutrition
• serious illnesses such as cancer or mental illnesses such as anorexia, etc.
  

At the latest, if your BMI is below 16 (severely underweight), you should see a doctor and get help. Being underweight not only leads to a lack of drive, weakness, feeling cold or concentration problems in the short term, but can also have serious long-term consequences for your health: bone loss (osteoporosis), infertility or damage to internal organs.

Therefore, if you have an underweight BMI, always make sure you eat a healthy diet that starts with a proper breakfast to help your weight return to normal.

BMI formula – normal weight

Normal weight is the weight at which most people are healthy and at which there is little increased risk of disease or health problems.

If your BMI is between 17.5 for women/18.5 for men and 24, you don't need to worry about losing or gaining weight, which is why it is often referred to as the “ideal” or “normal” value.

If your weight is outside this range, you should make sure you have a balanced, healthy diet and exercise in your daily routine to bring your BMI into a normal range.

BMI formula – overweight

From a BMI of over 25 (overweight) or over 30 (obesity), there is an increased risk of health problems.

However, a high BMI does not always automatically mean that you are overweight (e.g. in the case of athletes), as the BMI calculator does not take your body composition into account.

However, if you suspect that your body fat percentage is higher than your muscle mass, it is advisable to visit a doctor to clarify the high weight and to reduce weight by changing your eating habits and lifestyle.

Just like being underweight, being overweight or obese can lead not only to minor complaints such as sluggishness or aching limbs, but also to serious health problems such as type 2 diabetes mellitus, high blood pressure, arteriosclerosis (= vascular calcification) or even heart disease or heart attack.

There are three levels of obesity (severe overweight):

Obesity grade I, obesity grade II and obesity grade III.

When is the BMI formula not meaningful?

First of all: the BMI is only a guideline! The BMI does not always provide a reliable indication of your state of health, because factors such as the composition of your body mass, age, lifestyle, etc. are not included in the calculation. The BMI also says nothing about the exact distribution of body fat. But a lot of belly fat is considered a major health risk.

For whom is the BMI therefore less meaningful?

• People who do a lot of weight training and/or have a high muscle mass: muscles weigh more than fat, which means that a higher weight and consequently a higher BMI value is achieved faster. However, this value does not necessarily mean that you are overweight due to your body composition. Therefore, to get a better idea of your weight and health, a body fat analysis (BIA measurement) is recommended. More details at BMI for strength athletes and bodybuilders.
  
• Extremely small or large people
• Children and adolescents: The BMI table above is not suitable for people under 18 years of age, as they have their own reference values. There are special BMI tables for them (the so-called percentile curves) because they are still growing. Important: If your child is underweight or overweight, you should always consult your pediatrician.
  
• People over 60 years of age: Age is an important factor. As already briefly mentioned, a slight increase in body fat with increasing age is considered absolutely normal. At the end of the 1980s, the American National Research Council (NRC) found that the ideal BMI increases with age. The older you get, the higher your BMI can be. This means that the value of the normal weight increases for older people up to a BMI value of 29.
• The BMI values are not the same for all population groups. African Americans, for example, have a higher normal BMI, while Thais or Indonesians have a lower normal BMI than the Western population.
  

Important: In addition, it often makes sense to use a measuring tape to measure waist circumference if you have an elevated BMI. This should not be more than 88 centimeters for women and 102 centimeters for men.

Achieve an ideal BMI with a healthy breakfast

If your BMI is far from normal, first consider your lifestyle, your body composition and how healthy you feel. Do you know your daily calorie requirement?

If you still suspect that you are overweight or underweight, there is definitely a need for action. Nutrition counseling and sufficient exercise and sports are then important pillars for your health. Furthermore, it makes sense and is advisable to start the day with a healthy breakfast that will keep you full until your next main meal.

Ideally, this breakfast should contain lots of complex carbohydrates such as oats, which provide you with energy. Your healthy breakfast should also contain proteins and fats that help you feel full, e.g. nuts, avocado, seeds, dairy products.

Whether you want to gain, lose or maintain weight, a healthy breakfast will help you on your way and can support you in achieving your optimal BMI.

Healthy, sugar-free breakfast for an ideal BMI – find out more

Frequently asked questions

How do you calculate BMI with age?

The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m2). The following applies as a guideline: 19-24 years - BMI: 19-24, 25-34 years - BMI: 20-25, 35-44 years - BMI: 21-26, 45-54 years - BMI: 22-27, 55-64 years - BMI: 23-28, over 64 years - BMI: 24-29

How do I calculate my BMI?

The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m2). For example, the formula for a woman who is 1.60 m tall and weighs 52 kg gives a BMI value of 20.3. This indicates that the woman has a normal weight. An overview of BMI for women: BMI below 17.5 = underweight, BMI between 17.5 and 24 = normal weight, BMI between 25 and 29 = overweight, BMI between 30 and 35 = severely overweight.

What is the normal BMI for men of different ages?

If you are a man with a BMI between 18.5 and 24, you don't need to worry about losing or gaining weight, which is why we often talk about the “ideal” or “normal” weight. The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m2). Guide values: BMI below 18.5 = underweight, BMI: 18.5 - 24 = normal weight, BMI: 25 - 29 = overweight, BMI: 30 - 35 = severely overweight. The BMI is only a guide! The BMI does not always provide a reliable indication of your state of health, as factors such as body composition, age, lifestyle, etc. are not included in the calculation. Age is an important factor. A slight increase in body fat is considered perfectly normal with increasing age. The American National Research Council (NRC) found out in the late 1980s that the ideal BMI increases with age. The older you get, the higher your BMI can be. This means that the value of normal weight increases for older people up to a BMI value of 29.

What is the ideal body mass index?

The most important BMI values (according to the World Health Organization - WHO) are 17.5 to 24 for women and 18.5 to 24 for men, as these mark the range of normal weight and also the range of ideal weight. Normal weight is the weight at which most people are healthy and at which there is little increased risk of disease or health issues. The ideal weight can often be 1-3 kilos lower.

How do you calculate BMI?

The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m2). For example, the formula for a 1.60 m tall and 52 kg woman results in a BMI value of 20.3. This indicates that the woman is of normal weight. An example for a man: a man with a height of 1.85 m and a weight of 80 kg is still in the normal weight range with a BMI of 23.37. Calculation: 80 kg divided by (1.85 m times 1.85 m). 80 divided by 3.4225 = 23.37

What should someone who is 1.65 m tall weigh?

A woman of this height should weigh between 57 and 70 kilograms. This puts her in the normal range or only just in the overweight range.

What BMI at what age?

The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m2). The following applies as a guideline: 19-24 years - BMI: 19-24, 25-34 years - BMI: 20-25, 35-44 years - BMI: 21-26, 45-54 years - BMI: 22-27, 55-64 years - BMI: 23-28, over 64 years - BMI: 24-29. There are also small differences between men and women.

What is the right weight for my height?

The body mass index is a simple tool that quickly gives you an orientation about your own weight in relation to your height. The value is calculated using the formula “body weight in kilograms divided by height in meters squared” (kg/m2). For example, the formula for a woman who is 1.60 m tall and weighs 52 kg gives a BMI value of 20.3. This indicates that the woman has a normal weight. According to the WHO, the most important BMI values for women are 17.5 and 24, and for men 18.5 and 24, as these indicate the range of normal weight.