BMI Calculator

bmi calculator

The BMI calculator is the most widely used and simplest method of calculating the excess weight. However, it should be remembered that the BMI is a relative figure and that influencing characteristics such as gender, age, size, and fat or muscle tissue percentage are not taken into account when using the calculator.

As a result, the BMI calculator may become overweight in a person who does a lot of sport. His bodyweight alone indicates that the weight comes mainly from muscle and not from fat. 

BMI Introduction

The BMI, or Body Mass Index, is a formula for calculating weight about height. Furthermore, the BMI is calculated by multiplying the weight of the body in kilograms by the squared height in meters. Healthy weight ranges from 18.50 to 24.90 BMI.

A BMI of less than 18.50 means you’re underweight, while a BMI of 18.50 to 24.90 means you’re at a healthy weight. In addition, anyone with a BMI of 25 or above is considered overweight, while those with a BMI of 30 or higher are termed obese (obesity). In this case, a doctor should be consulted.

BMI Categories

The body mass index – BMI for short – is a parameter that helps determine whether weight and height are in a medically healthy relationship to one another or whether the person is, for example, very overweight, i.e. obese. However, the World Health Organization (WHO) divides the BMI into six different classes:

Under 18.50Underweight
18.50 – 24.90Normal Weight
25.00 – 29.90Overweight / Pre-obese
30.00 – 34.90Grade I Obesity
35.00 – 39.90Grade II Obesity
Over 40.00 Grade III Obesity

Body Fat Percentage

The BMI also says nothing about the distribution of body fat. In particular, too much belly fat is considered a health risk. Other classifications include age and gender in the assessment. For example, with increasing age, the metabolism and body composition change. The individual weight to be aimed for also depends on age, gender, and other information. Your doctor will help you determine the right weight for you. 

Many experts now consider the value “waist circumference in centimeters divided by body height in centimeters” to be more meaningful. A value below 0.5 (below 0.6 for older people) is desirable here. The waist circumference alone also helps for rough orientation: it should not be more than 102 centimeters for men and 88 centimeters for women.

Check: Body Fat Calculator

BMI Calculator with Age

Age also plays a decisive role: it has meanwhile been found that a slightly higher BMI value can be beneficial for health in old age. However, the body can fall back on small fat deposits, which it needs to survive longer illnesses. For this reason, you should only use the result of the BMI calculator as a guide and relate your body mass index to your gender, fitness, and age.

To be able to give a better assessment of your weight, age must be taken into account in addition to weight and height. 

Age is relevant because the normal weight shifts as you get older. From around the age of 40, the metabolism and body composition change. The result: We gain weight naturally, so the normal weight shifts and with it the recommended BMI. However, bodyweight can fall again with advancing age, because older people lose more muscle mass, which is heavier than fat. This leads to a lower weight so that the BMI of older people of normal weight can incorrectly indicate that they are underweight.

BMI Calculator for Children

There are separate rules for children. Moreover, there are special BMI tables here and the BMI can only be viewed as a guide, as they are still growing. If you have the feeling that your child weighs too much or too little, it is best to talk to your pediatrician about it. Do not just put the child on a diet.

The Formula for BMI Calculator

The BMI is calculated using the following formula:

Bodyweight (in kgs) / body height (in meters) squares.

This formula should be made even clearer by a calculation example: let’s say you are 1.83 meters tall and 65 kgs.

We will have: 1.83 x 1.83 = 3.35

Now divide your weight by this value: 65/ 3.35 = 19.40

19.49 – or rounded up to 19 – is your body mass index (BMI).


BMI is a helpful tool for figuring out how to classify your weight. However, you should not exaggerate the result and, if in doubt, get medical advice from a doctor you trust. The biggest issue in BMI is that it doesn’t differentiate between muscle and fat mass.

Frequently Asked questions

What is BMI?

The body mass index, or BMI for short, is the most often used formula for calculating the weight. Mathematically, the square root of the ratio of body weight in kilograms to body height in meters is used to calculate it.

BMI = body weight / (height) ²

An example: A 40-year-old man with a bodyweight of 85 kgs and a height of 1.83 meters has a BMI of 46.45 and is therefore of grade III Obesity.

With our BMI calculator, you can quickly see if your weight is in the healthy range. This is based on the conventional formula, but it also considers age.

How to Calculate BMI?

How do you calculate your BMI? It’s very straightforward. The following is the formula for calculating BMI:

BMI = body weight / (height) ²

E.g.: A man weighs 70 kg and height of 1.67m.
Calculation: (70 kgs) / (1.67 meters) ² ≈ 42
Therefore, the man has a BMI of 42.

How to Figure BMI Calculator

Children’s and adolescents’ body fat percentages change over time, depending on their age and gender. A BMI of 20 for a 7-year-old child would be considered overweight or obese, whereas a BMI of 20 for a 12-year-old child would be considered normal weight.

Special BMI standard value curves, known as percentile curves, have been devised to determine the body weight of children and adolescents. They illustrate how many children or adolescents of the same age and gender fall below this threshold. This is how it would be interpreted: If an 8-year-old girl’s body weight is in the 70th percentile, it signifies that 70% of girls her age have lower body weight and 30% have higher body weight.

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