BMI Calculator

Why one body gets two different verdicts

The reason this page shows two scales is that the same number is read differently depending on which population the thresholds were built from. Studies in Asian populations found that metabolic risk — blood pressure, blood sugar, blood lipids — tends to rise at a lower body mass index than the global thresholds assume, and Korean clinical practice follows the lower Asia-Pacific boundaries as a result.

The practical consequence is confusing the first time it happens: a figure that reads as comfortably normal on a chart at home can be labelled overweight on a Korean clinic printout without anything about your body having changed. Which scale applies to you is a clinical judgement rather than a passport question, but if you are being assessed in Korea, expect the Korean one to be on the paperwork.

Where this number actually turns up in Korea

• Health checkups. Height, weight and the resulting index are recorded as routine at Korean clinics and at national or employer screening appointments. The report generally flags a category without explaining how it was chosen.
• Gym body-composition scales. Machines that print a receipt covering body fat, muscle mass and this index are everywhere in Korean gyms. The index line is the least sophisticated figure on that sheet, so read the rest.
• Clothing, not at all. It predicts nothing about fit. Korean sizing tends to run narrow through shoulders and hips independently of weight, so use a size chart instead.

What the number cannot see

This is height and weight and nothing else. It cannot separate muscle from fat, so trained athletes routinely land in an overweight band while someone carrying little muscle can sit mid-range with a lot of internal fat. It also ignores where weight sits, which is why clinicians pair it with a waist measurement — abdominal fat carries risk that a single index figure hides completely.

Situations where the result is misleading enough to set aside:

• Children and teenagers, who are assessed against age- and sex-specific growth percentiles rather than adult categories.
• Pregnancy, where weight gain is expected and the usual bands do not apply.
• Older adults, where muscle loss can pull the number down while health declines.
• Very tall or very short people, because the formula squares height and drifts at the extremes.

Reading your result sensibly

Treat it as one screening signal among several rather than a score. A single reading says little; the direction of change over months — measured on the same scale, at a similar time of day — says considerably more. If your figure lands close to a boundary, remember how easily it moves: a couple of centimetres of mis-measured height shifts the category, so measure without shoes with your heels and back against a wall, and don't redo the calculation after a heavy meal expecting meaning from the difference.

This calculator is for general information only. It is not a medical diagnosis and not a substitute for advice from a doctor or other qualified health professional.

Frequently asked questions

Why is my BMI normal at home but overweight in Korea?
Korean clinics apply the Asia-Pacific thresholds, which sit lower than the global WHO bands because health risks have been observed to rise at a lower index in Asian populations. Your body has not changed — only the reference scale being applied to it has.

Which scale should I use, the WHO one or the Asian one?
If you are being screened or treated in Korea, the Korean scale is the one your results will be judged against. Outside that context, reading both as a range is more informative than picking one, and a doctor can tell you which fits your background.

Is BMI accurate if I lift weights?
No, not on its own — muscle is denser than fat, so strength-trained people are frequently pushed into an overweight category while being metabolically healthy. Body-fat percentage and waist measurement describe that situation far better.

Can I use this for my child?
No. Children and adolescents are assessed with age- and sex-specific percentile charts rather than the fixed adult categories shown here, so an adult calculation can give a badly misleading answer for a growing body.