Calculate BMI

Calculate adult body mass index from kilograms and metres and place it in the WHO screening bands.

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ToolBMI Calculator
Input
Output
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Preview

How it works

Kilograms are divided by metres squared and the quotient is rounded to one decimal place. Adult thresholds label values below 18.5 as underweight, 18.5 to 24.9 as normal weight, 25 to 29.9 as overweight, and 30 or more as obese; height and weight have no fabricated defaults.

Formula
BMI = weight in kilograms ÷ height in metres²
  • The 1.2-to-2.6-metre height range catches many centimetre-as-metre mistakes.
  • This is a population screening ratio rather than a direct measurement of fat, muscle, or health.

Worked example

Normal BMI
Calculate BMI for a 70 kg person who is 1.75 m tall
Input
											Weight: 70
Height: 1.75
Output
												Weight: 70 kg
Height: 1.75 m
BMI: 22.9
Category: Normal weight

When to use this

WHO surveillance groups adult populations by BMI, primary-care records use it alongside history and other measurements, and longitudinal weight records recalculate it as weight changes at a stable adult height.

Edge cases

  • A height entered as 175 instead of 1.75 is rejected by the adult metre range rather than producing a near-zero BMI.
  • Children and adolescents require age- and sex-specific growth references, but age is not collected, so only adult bands are displayed.
  • Pregnancy, oedema, amputation, and high muscularity receive no body-composition correction and can make the ratio unsuitable for individual interpretation.

References