The weight index is used to assess the relationship between a person’s weight and height.

You can calculate your own body mass index using the Bodymaja calculator.

**What is a good body mass index?**

The Body Mass Index (BMI) is a traditional measure of health that identifies whether a person is of normal weight or whether they may be underweight, overweight or obese.

The BMI helps to catch potential health risks early.

Being significantly overweight increases your risk of getting sick various diseasessuch as diabetes, cancer, sleep apnoea, high blood pressure or cholesterol.

Being underweight can again lead to health risks such as malnutrition, compromised immune defence, osteoporosis, infertility and impaired growth and development in children and adolescents.

**How is the adult body mass index calculated?**

The formula for calculating the weight index is the weight of a person divided by the square of their height.

In this case, the following formula is used:

**Body mass index (BMI) = weight / height²**

When calculating the weight index, it is important to remember that weight is expressed in kilograms and height in metres.

So, for example, if you are 175 cm tall and weigh 70 kg, your body mass index is calculated as follows:

70 / 1,75² = 70 / (1,75*1,75) = 70 / 3,0625 = 22,9

**Weight Index Calculator**

You can calculate your own body mass index using the formula above.

Alternatively, you can find out your BMI by entering your height and weight into the BMI calculator below, which will do the calculation for you.

### New body mass index calculator developed by Trefethen

**Nick Trefethen**, Professor of Numerical Analysis at Oxford University, developed in 2013 a new formula to calculate the body mass index.

His formula takes better account of the distortion caused by, among other things, height.

The formula is therefore better able to identify overweight short people and, conversely, tall people who are actually slim.

He says it also gives a closer-to-reality assessment of human shape and size.

Using the formula developed by Trefethen, the weight index is calculated as follows:

1.3 x weight (kg) / length^2,5 (m).

This calculator also expresses weight in kilograms and length in metres.

So, for example, if you are 175 cm tall and weigh 70 kg, your body mass index is calculated as follows:

1,3 x 70 / 1,75^2,5

In the formula developed by Trefethen, a weight factor of 1.3 is the square root of the average human height of 1.69 metres.

He justifies the power of 2.5 in the formula by the fact that humans are not two-dimensional, so why should weight be calculated on this basis.

You can easily calculate your body mass index according to this formula using the calculator below.

**What is a normal body mass index?**

Once the body mass index has been calculated, it is compared with the figures in the BMI table.

This shows whether the person is underweight, normal weight or overweight.

The body mass index is considered normal when it is between 18.5 and 24.9.

Based on this interpretation, it is possible to make informed decisions about lifestyle changes to improve the situation.

Body mass index |
Classification |
Risk of adverse health effects |

All 18.5 | Underweight | High |

18,5-24,9 | Normal weight | Low |

25,0-29,9 | Mild overweight | Low to moderate |

30,0-34,9 | Significant overweight | High |

35,0-39,9 | Severe overweight | Very high |

40 or more | Morbid overweight | Very high |

**Body mass index for children and adolescents**

The body mass index for children and adolescents is calculated in the same way as for adults, but age is taken into account in the results.

For children, it is always worth discussing the interpretation with a doctor if there are concerns about the child’s weight or growth curves.

When interpreting the body mass index of children and adolescents, it should be noted that the normal range of the body mass index for these age groups is different from that of adults.

The reference values change up to the age of 18 and only after that are constructed using the adult formula.

**The limitations of the BMI – what doesn’t the BMI tell you? **

Although the body mass index is a widely used measure of health status, it does not provide an overall picture a person’s health, as it does not take into account other factors that affect a person’s health.

The BMI does not take into account factors such as a person’s age, gender, genetic make-up, muscle mass or the amount of fat and its distribution in the body.

It may also not work for as a reliable indicator for pregnant women, athletes or elderly people.

For these reasons, the figure provided by the body mass index calculator should be viewed critically, although it does provide an important guide to assessing your health.

To get a more comprehensive and individualised picture of your own health, it is therefore advisable to take a detailed body composition measurement.