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BMI Calculator

Calculate BMI from height and weight, follow the formula and understand WHO adult categories and their limitations.

Available

Inputs

Enter values

Live
iHeight without shoes in centimetres.
cm

Height without shoes in centimetres.

iBody weight in kilograms.
kg

Body weight in kilograms.

Load example

Explanation

How BMI Calculator works

The BMI calculator relates body weight to height and uses WHO adult categories for orientation. It makes the calculation transparent but does not provide a diagnosis.

Formula and interpretation

Body mass indexBMI = Gewicht (kg) / Körpergröße² (m²)

Convert centimetres to metres before squaring height.

For adults, WHO distinguishes values below 18.5, 18.5 to below 25, 25 to below 30, and 30 kg/m² or above. Population thresholds are not an individual health diagnosis.

Practice

Practical examples

70 kg at 1.75 m

An adult is 175 cm tall and weighs 70 kg.

Result: BMI = 70 / 1.75² = 22.9, within the WHO adult reference range.

90 kg at 1.80 m

An adult is 180 cm tall and weighs 90 kg.

Result: BMI = 90 / 1.80² = 27.8, above the WHO adult reference range.

Notes

Common mistakes

  • Squaring centimetres directly

    Height is entered as 175 instead of 1.75 metres.

    Divide centimetres by 100 before squaring the metre value.

  • Treating BMI as a diagnosis

    One number is read as a complete assessment of health or body fat.

    Use BMI only as rough orientation alongside individual factors.

  • Applying adult cut-offs to everyone

    Adult WHO thresholds are applied unchanged to children or pregnancy.

    Use the appropriate professional method for special groups.

FAQ

Frequently asked questions

What does BMI indicate?

BMI relates weight to height. It is a rough screening and orientation value, not an individual diagnosis.

How is BMI calculated?

Weight in kilograms is divided by height in metres squared.

What is the adult BMI reference range?

WHO classifies 18.5 to below 25 kg/m² as normal weight in adults, 25 and above as overweight, and 30 and above as obesity.

Is this calculator suitable for children?

No. Children and adolescents require age- and sex-specific BMI-for-age growth references.

Can BMI be interpreted this way during pregnancy?

No. Weight changes in pregnancy require pregnancy-specific professional assessment.

What about high muscle mass?

BMI does not distinguish fat, muscle and bone and may appear high in very muscular people.

What about older adults?

Body composition changes with age, so the same BMI may conceal different proportions of muscle and fat.

Why does the calculator not ask for age or sex?

The adult BMI formula uses only height and weight. Age and sex would not change the calculation without another assessment method.

How should height and weight be measured?

Measure without shoes, standing straight, and with a suitable scale. Clothing and time of day can affect weight.

Does the result replace a medical examination?

No. Symptoms, major or unintended weight changes and individual risks need professional assessment.

Limits

Limitations

  • BMI does not distinguish fat, muscle, bone mass or fat distribution.
  • The classification is only rough adult guidance, not for children or pregnancy.
  • The result is not a diagnosis and does not replace individual medical assessment.

Sources

Sources and references

  • Obesity and overweightWorld Health Organization (WHO)

    Defines the BMI formula and adult overweight and obesity thresholds, while pointing to age-specific child standards.

    View source
  • Physical status: the use and interpretation of anthropometryWorld Health Organization (WHO)

    WHO technical report on the use and interpretation of anthropometric measures including BMI.

    View source
  • Overweight and obesity in adultsNational Health Service (NHS)

    Explains that BMI cannot distinguish muscle from fat and therefore has interpretive limits.

    View source

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