Body Mass Index (BMI)

BMI Calculator - What is your Body Mass Index?

With the BMI calculator you can calculate your BMI. Actually, the Body Mass Index, which is hidden behind the abbreviation BMI, is a measure for evaluating your weight in relation to your height. The BMI calculator also helps you assess your current weight based on your gender and age. BMI is calculated as follows: BMI = weight in kilograms / (height in metres)². BMI is thus measured using the International System of Units (SI) in kiolgrams and metres. Converted into Anglo-American units, the formula for BMI is: 703 × weight in lbs / (height in inches)². However, this measurement alone is not enough; the correct evaluation of the BMI, taking into account gender and age, is crucial. Only then can your weight be classified and the most important question answered: are you underweight, normal weight or overweight? The BMI calculator also helps you find your ideal weight.

The most important topics on the BMI calculator

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Input 'Help' for the BMI Calculator

In the following you will find information on the individual input fields of the BMI calculator

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Units of measurement

BMI Calculator: unit of measurement Please select the appropriate units of measurement.


By selecting 'US/UK' Anglo-American units of measurement are taken into account. Pounds (lbs) are used for weight and feet (ft) or inches (in) are used for height.


After selecting 'Metric' metric units of measurement are taken into account. Kilograms (kg) are used for weight and centimetres (cm) are used for height.


BMI Calculator - Weight Please enter your weight in kilograms. When calculating the BMI, your weight is put in relation to your height.


BMI Calculator - Height Please state your height in cm, because the BMI formula and calculation determines your height based on your weight.


BMI Calculator - Age Please state your age. The assessment of your weight by BMI is age-dependent - weight usually increases with age. A slight excess of normal weight with increasing age is considered harmless, especially since a certain amount of fat is not considered unhealthy. Fat reserves protect the body in times of crisis - in old age it is important to avoid emaciation due to illnesses or a lack of appetite. For children and adolescents there are other ideal values for BMI – this calculator here is reserved for adults!


BMI Calculator - Gender Please indicate your gender. The assessment of your weight by BMI is gender-dependent, because men have a different physique than women. Their proportion of muscle to total mass is higher than that of the female sex.

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BMI Assessment by Age and Sex

Once the BMI has been determined using the BMI formula, it still needs to be assessed. It is part of human nature to standardise things - to define a standard and compare others to it. As early as the 19th  century, the Belgian scientist Adolphe Quetelet developed a formula, the Quetelet formula. This formula was named after him, with the help of which the standard format of our body can be described in terms of weight and size. It was revived a good 100 years later, in 1972, when the American psychologist Ancel Keys rediscovered it and gave it the name BMI Calculation.

Even today, the World­Health­Organisation WHO still uses weight classification for research purposes. WHO still uses BMI to classify weight for research purposes, regardless of age and gender. Other organisations, however, differentiate the individual classes. For example, the German Nutrition Society DGE takes the influence of weight into account in a gender-dependent calculator, while the American National Research Center also includes age in an age-dependent calculation.

Below you will find the corresponding tables for the assessment of BMI for adults, which are also used by our BMI calculator for the interpretation of BMI.

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BMI classification of the German Nutrition Society (gender-dependent)

Underweight< 20< 19
Normal weight20-24.919–23.9
Severe overweight30-34.930–34.9
Grad II Adiposity35-39.935–39.9
Grad III Adiposity≥ 40≥ 40
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BMI classification according to American National Research Center (age-dependent)

AgeIdeal BMI
> 6524–29

What other readers have also read

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Example of BMI Calculation and Assessment

Mr Dittrich would like to determine his BMI and use it to find out how his weight is assessed. He is

  • Weighing 180 lbs,
  • 5 feet 9 inches in height, and
  • 60 years old.
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Calculation of Mr Dittrich's BMI

The general BMI formula is:

BMI = weight in kg / (height in m)²

Translated to the Anglo-American units, the formula is

703 × weight in lbs / (height in inches)²

According to this BMI formula, Mr Dittrich's BMI is calculated as follows:

703 × 180 lbs / (5 feet 9 inches)² =
703 × 180 lbs / (69 inches)² = 26.58

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Assessment of the BMI of Mr Dittrich

According to the age-independent BMI classification of the German Nutrition Society, Mr Dittrich's BMI of 26.58 is above normal weight (BMI 20.00 to 24.99). However, body weight usually increases with age. This is taken into account in the classification of the American National Research Council (NRC). Exceeding the normal weight (in Mr. Dittrich's age up to BMI 28.00) is therefore considered harmless. This results in the following assessment of Mr Dittrich's BMI:

Mr Dittrich is of "age-related" normal weight.

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General Division of the Weight Classes

In general, the classifications have relatively wide ranges for underweight, normal weight and the different forms of overweight. Attention is rightly focused on severe overweight with the levels of obesity I, II and III. The greater the deviation from the ideal weight, the greater the health risks. In highly developed industrialised countries, there are more and more people who are too fat. Their limited mobility adversely affects their quality of life. Obese people suffer more frequently from heart and circulatory diseases, diabetes and strokes. In addition to health problems, social exclusion leads to psychological discomfort. Therefore, consider your BMI as a rough guide – and if in doubt, talk to your doctor about reducing your weight. with your doctor.

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Limitations in BMI Weight Assessment

In recent years, the assessment of BMI has come under some criticism. It takes too little account of the individual's physique, and weight is overrated as a measure of a healthy life. For example, the weight of competitive athletes, bodybuilders, pregnant women and breastfeeding mothers cannot be calculated with the BMI calculator.

If, for example, a 25-year-old athlete with a body weight of 220 lbs and a height of 5 feet 9 inches reaches a BMI of 32.49, which is extremely high. The table shows him as severely overweight (obesity I). You can't tell by looking at him, because he looks well-trained and healthy. His fat content is less than 20 per cent, and his muscles make up a correspondingly high proportion of his total mass. The results of his medical tests also confirm his good health.

In this view of one's own weight, the distribution of body fat does not play a significant role. However, it is precisely abdominal fat that is suspected of promoting serious diseases.

In the BMI formula, weight is crucial. As a result, some young people starve themselves into anorexia. In addition to heart and circulatory diseases, kidney damage and gastrointestinal problems, the associated malnutrition can lead to osteoporosis, tooth loss and anaemia.

When deciding whether or not children and adolescents are overweight, parents and doctors must take special care. For the assessment of their weight, so-called percentile curves (reference curves) should be taken into account. Please visit our BMI calculator for children and adolescents who have submitted their reference curves.

For an initial decision on whether your weight is ideal or whether you should do something to lose weight, our BMI calculator offers exactly the right advice. If you are overweight, you should eat healthier and exercise more. Feel free to calculate what your ideal weight should be. If your BMI is already in a very low range, be careful not to slip into anorexia. A diet rich in protein and endurance or weight training will help you build more muscle and still stay healthy. However, you should also include other values such as the percentage of fat in your total mass in your assessments of your current weight.

Source information

As source for the information in the 'Body Mass Index' category, we have used in particular:

Last update

This page of the 'Body Mass Index' category was last edited or reviewed by Stefan Banse on February 20, 2023. It corresponds to the current status.

Changes in this category "Body Mass Index"

  • Editorial revision of this page