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BMI Calculator

Calculate Body Mass Index from height and weight, and see which standard category it falls in.

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What BMI Calculator does

BMI is weight in kilograms divided by height in metres squared. It was devised in the nineteenth century as a way of describing populations, and it became a clinical screening tool because it needs only two measurements that are easy to take.

It is a screening indicator, not a diagnosis. It says nothing about body composition, fat distribution or fitness, which is why it misclassifies some people badly.

  • BMI from weight in kilograms and height in centimetres
  • Standard adult category for the result

How to use BMI Calculator

  1. 1

    Enter your height in centimetres

    Measure without shoes for an accurate figure.

  2. 2

    Enter your weight in kilograms

    Weigh at a consistent time of day; normal fluctuation is a kilogram or two.

  3. 3

    Read the value and its category

    The standard adult bands are under 18.5, 18.5 to 24.9, 25 to 29.9, and 30 or above.

Limits and known behaviour

  • BMI cannot distinguish muscle from fat. A muscular athlete is routinely classified as overweight or obese despite very low body fat.
  • It ignores where fat is carried, and abdominal fat carries more metabolic risk than the same weight elsewhere. Waist measurement adds information BMI cannot.
  • The standard thresholds were derived largely from European populations. Some health bodies use lower thresholds for people of South Asian descent, where metabolic risk appears at a lower BMI.
  • Adult categories do not apply to children or adolescents, who are assessed on age and sex percentile charts.
  • It is not appropriate during pregnancy, or for people with significant fluid retention.
  • Metric units only: kilograms and centimetres.
  • This is an estimate from a published formula, not a medical assessment. It cannot diagnose anything, and it is no substitute for advice from a clinician who knows your history.

Privacy and data handling

Runs entirely in your browser

  • Every figure you enter stays in this page. Your height and weight is not transmitted, logged or stored anywhere.
  • There is no account, no saved history and no autosave: reloading the page clears the form.

Site-wide data handling, including analytics and advertising, is described in the privacy policy.

Frequently asked questions

Is BMI accurate for me?

It is accurate as a calculation and limited as an indicator. It works reasonably across a population and can be quite wrong for an individual, particularly if you are very muscular, very tall, very short, elderly, or pregnant.

What should I do with the result?

Treat it as one data point. A trend in your own BMI over time is more informative than a single reading, and a waist measurement alongside it tells you more than either alone.

Why do some sources use different thresholds?

Because risk at a given BMI varies by population. Several health authorities recommend lower overweight and obesity thresholds for people of South Asian, Chinese and other Asian descent.