BMI Calculator

What to type in, and which scale to pick

Weight in kilograms and height in centimetres, unless you switch to imperial, in which case weight is in pounds and height is total inches (five foot five is 65, not 5.5). The third box is the one that was missing from the older version of this page: the cut-off scale.

• WHO international is the chart printed in every Western textbook and built into most fitness apps. Overweight starts at 25, obese at 30.
• Indian / Asian is the chart your physician in Pune or Kochi is more likely to be reading from. Overweight starts at 23, obese at 25. This is the consensus that Indian endocrinologists published in 2009, and it is what ICMR and the national diabetes programme work with.

The healthy weight range and the distance-from-range figure both follow whichever scale you picked, so changing that one dropdown changes three of the four results.

One man, two verdicts

The calculator opens with a 70 kg man at 165 cm, which is close to the average urban Indian male build.

BMI = weight (kg) / height (m)²
    = 70 / (1.65 × 1.65)
    = 70 / 2.7225
    = 25.71

	WHO scale	Indian scale
BMI	25.7	25.7
Category	Overweight	Obese
Healthy weight range	50.4 kg – 67.8 kg	50.4 kg – 62.3 kg
Distance from range	2.2 kg	7.7 kg

Same person, same number. On the WHO chart he is a couple of kilos over, the sort of thing a doctor mentions in passing on the way out. On the Indian chart he is obese and about 7.7 kg above where the chart wants him. Neither reading is wrong. They answer different questions. The WHO chart asks at what BMI Europeans start getting sick; the Indian chart asks the same about us.

A 62 kg woman at 155 cm gets a BMI of 25.8 and the same split: overweight on one scale, obese on the other.

Why the Indian line sits two points lower

The WHO cut-offs came out of European and North American mortality data in the 1990s. When they were applied in India, Sri Lanka and among South Asians in Britain, the same BMI kept showing up with more body fat, more of it inside the abdomen, and diabetes appearing at weights those charts called normal.

Three things drive that.

More body fat at the same BMI. An Indian man at a BMI of 23 carries roughly the body fat a European man carries two or three points higher. Smaller frame, less muscle, more adipose tissue. The scale looks fine; the composition does not.

Central obesity. The fat settles around the waist and inside the abdomen rather than on hips and thighs, and visceral fat is the kind that drives insulin resistance.

Diabetes that arrives early. Type 2 diabetes in India routinely appears a decade earlier and at a lower BMI than in the West. Moving the overweight line to 23 and the obesity line to 25 moves the screening net to where the risk actually is.

The WHO itself later published Asia-Pacific guidance with these lower cut-offs, and the Indian consensus group adopted 23 and 25 outright. So when a corporate health check-up report says “overweight” against a BMI of 23.5, the lab is using the Indian chart. It is not a mistake, and it is not the lab trying to sell you a wellness package.

The waist measurement BMI cannot see

BMI is height and weight. It has no idea where the weight sits. For Indians the more telling number is a tape at the navel:

	Action line used in India	Western equivalent
Men	90 cm	102 cm
Women	80 cm	88 cm

A man of 64 kg at 170 cm has a BMI of 22.1 and passes on both charts. If his waist is 94 cm he still has the pattern that sends people to the diabetologist at 45. That is the “thin-fat Indian”, and the body fat calculator is built around exactly that tape measurement, so run it after this one if your waist is anywhere near the line.

Measure standing, at the navel, after breathing out, not at the trouser waistband, which sits lower and reads smaller. A size 34 trouser is usually a real waist of 90 cm or more. I have watched people argue with a nurse over this and lose.

Where BMI goes wrong in practice

Muscle. Someone who lifts three times a week can sit at 27 with a flat stomach. BMI counts the muscle as fat. The waist and the body fat calculator sort this out; BMI never will.

Age. Past about 65 a slightly higher BMI goes with better outcomes, and the adult bands were never meant for children or for anyone pregnant. Growth charts and antenatal norms are separate things.

The line itself. 24.9 and 25.1 are the same body. The bands are administrative lines drawn through a continuous risk. The line an insurer uses to load your premium is a business decision on top of that; several Indian insurers start loading around a BMI of 30 on the WHO scale, and the medical at the time of buying the policy is where it gets applied. If you are near a line, know which chart they are using before you sign.

Height in the wrong unit. Five foot five typed as 5.5 is rejected. 165 typed in the imperial box is treated as 165 inches and rejected too. If the result looks absurd, that is nearly always why.

Trusting one reading. Weight swings a kilo or more between morning and evening, more after a wedding weekend. Weigh in the morning, after the toilet, before breakfast, and take the weekly average.

If the question is what you should weigh rather than what band you fall in, the ideal weight calculator puts four formulas next to the healthy BMI range. If the question is what to eat to get there, start with the calorie calculator, which uses the same height and weight and turns them into a daily target.