Calculators
BMI calculator
BMI is a population screening tool, not a diagnosis. It cannot tell muscle from fat, which is why a trained athlete and a sedentary person of the same height and weight get the same number.
| Category | BMI |
|---|---|
| Underweight | < 18.5 |
| Normal | 18.5 – 24.9 |
| Overweight | 25 – 29.9 |
| Obese | ≥ 30 |
How to use it
- Enter your height in centimetres and weight in kilograms.
- Read your BMI and the WHO category it falls into.
- The healthy weight range shows what you would need to weigh for a BMI of 18.5–24.9.
- Use it as a rough signal, not a verdict.
The thresholds are not universal
The WHO's international cut-offs are 25 and 30, but its Asia-Pacific guidance uses 23 and 27.5, and China's national standard sets overweight at 24 and obesity at 28. The reason is that the same BMI corresponds to different body-fat percentages across populations. A BMI of 26 is “overweight” under one standard and comfortably inside “normal” under another, which is why the single number says less than it appears to.
What it measures, and what it misses
BMI is weight divided by height squared. It says nothing about where fat is stored, and visceral fat around the organs is the component most strongly linked to metabolic risk. A person with a “normal” BMI and high visceral fat can be at greater risk than someone classed as overweight with a muscular build. Waist-to-height ratio is a cruder but better single number for that specific question.
What the number is good for, and what to use instead
BMI is a population statistic applied to an individual. It cannot tell muscle from fat, and it systematically misreads very tall and very short people because the denominator squares height. A waist-to-height ratio above 0.5 is a better single-number proxy for cardiometabolic risk, and it needs a tape measure rather than a scale.
The useful signal is the trend, not the reading. Weighing weekly under similar conditions and watching the direction over three months tells you more than any single day's classification — water varies by two kilos across a day.
Frequently asked questions
What are the BMI categories?
Under 18.5 is underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese. These thresholds are WHO values for adults of any sex.
Why can BMI be misleading for athletes?
Muscle is denser than fat, so a muscular person can register as overweight while carrying very little fat. The measure was designed for populations, not individuals.
Does it work for children?
No. Children and teenagers are assessed on age-and-sex percentile charts, not fixed cut-offs. This calculator follows adult thresholds only.
What is BMI Prime?
Your BMI divided by 25, the top of the normal band. A value under 1 means you are below the upper limit; it is a quick way to see how far you sit from it.
Does BMI work for children?
No. Children are assessed on age- and sex-specific percentile curves, because body composition changes continuously as they grow.
Which BMI thresholds should I use?
WHO global: 25 / 30. WHO Asia-Pacific: 23 / 27.5. China: 24 / 28. The difference reflects population-level risk, not a measurement error.