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A calculator based on scientific references

Know your BMI for your age

Enter your measurements once. We will automatically use the appropriate World Health Organization classification: the age- and sex-specific reference from 5 to 19 years, and the adult classification from age 20.

No result appears until you press “Calculate BMI”.

BMI is the first step. Let's calculate it properly together.

Calculate your BMI

Age selects the correct reference, and sex is required only from 5 to 19 years.

Enter measurements

Use completed age, height in centimetres, and weight in kilograms.

years
Required only from 5 to 19 years.
cm
kg

BMI result

The result appears only after pressing the calculate button.

BMI — Your result will appear here
Age category
—
Reference used
Enter your data, then press “Calculate BMI”

How it is calculated

The same formula, interpreted for age

BMI = weight in kilograms ÷ height in metres squared. The formula is the same for everyone, but interpretation changes with age; from ages 5 to 19 it also changes with sex.

20+

Adults from age 20

BMI is compared directly with the World Health Organization adult cut-offs.

  • UnderweightBelow 18.5
  • Normal weight18.5 to 24.9
  • Overweight25 to 29.9
  • Obesity class I30 to 34.9
  • Obesity class II35 to 39.9
  • Obesity class III40 or above

5–19

Children and adolescents

BMI is converted to a Z-score using the child’s age and sex under the WHO 2007 reference.

  • Severe thinnessBelow -3 SD
  • Thinness-3 to below -2 SD
  • Healthy weight for age-2 to +1 SD
  • OverweightAbove +1 to +2 SD
  • ObesityAbove +2 SD

References

The science behind the calculator

These are the studies and references used for the formula and classifications. Select a reference name to open the original source.

  1. WHO BMI-for-age reference (5–19 years)

    The official source for the standard-deviation cut-offs and age- and sex-specific tables used for children and adolescents.

  2. de Onis et al. — Development of the WHO 2007 growth reference

    The peer-reviewed study explaining the international growth reference for school-aged children and adolescents.

  3. WHO Technical Report 894 for adult BMI classification

    The reference used to divide BMI into six adult categories from age 20.

  4. Keys et al. — Indices of relative weight and obesity

    The study that evaluated BMI and supported its use as a population-level relative-weight index.