A 35-year-old man who is 175cm and 78kg has a BMI of 25.5. Read against Korea's guideline that is obesity, class I. Read against the World Health Organization's, it is overweight. Same body, one category apart.
1. What it gives you. The calculator below judges on the Korean scale used by the Korean Society for the Study of Obesity and the KDCA, and returns your basal metabolic rate and daily calorie needs alongside it.
2. What it changes. Korea's thresholds sit two steps below the WHO's — overweight at 23 vs 25, obesity at 25 vs 30. Read an English-language source at face value and you get “BMI 27 isn't obese yet.” And BMI cannot tell muscle from fat.
3. How to use it. Enter your waist too — the KDCA thresholds are 90cm for men and 85cm for women. A normal BMI with a large waist is the more common case, and BMI alone walks straight past it.
Calculates automatically. BMI categories follow the Korean Society for the Study of Obesity (2022) guideline; BMR uses the Mifflin-St Jeor equation. This is a reference estimate that cannot account for muscle mass or body fat, and is not a medical diagnosis.
What the six output rows actually are
The rows are not all the same kind of number. Some are official thresholds; some are statistical estimates. Mixing them up is where people go wrong, so they are separated here.
| Output | Example | Where the number comes from |
|---|---|---|
| BMI | 25.5 | Weight ÷ height(m)² — the same everywhere |
| Category | Obesity class I | Korean guideline (KSSO / KDCA) |
| Healthy weight range | 56.7 – 70.1 kg | BMI 18.5–22.9 converted back at this height |
| Basal metabolic rate | 1,704 kcal | Mifflin-St Jeor equation (1990) — an estimate |
| Daily maintenance | 2,343 kcal | BMR × activity factor 1.375 — an estimate |
| Weight-loss target | 1,843 kcal | Maintenance − 500 kcal (0.5 kg per week) |
The first three rows are values that come from official documents. From basal metabolic rate down, they are equations fitted to population data. Two people with identical inputs can burn noticeably different amounts.
Korea's thresholds sit two steps below the WHO's
This is the single most common source of confusion, and the reason an English-language article might tell you a BMI of 27 is “not obese yet”.
| Category | WHO | WHO Asia-Pacific · Korean Society for the Study of Obesity |
|---|---|---|
| Overweight / pre-obesity | BMI 25+ | BMI 23+ |
| Obesity | BMI 30+ | BMI 25+ |
Hence the same 25.5 being “overweight” on the WHO scale and “obesity class I” on the Korean one. The thresholds were lowered because, at a given BMI, Asian populations tend to carry more body fat and meet metabolic risk earlier.
The full Korean scale:
| Category | BMI | At 175cm |
|---|---|---|
| Underweight | Below 18.5 | Under 56.7kg |
| Normal | 18.5 – 22.9 | 56.7 – 70.1kg |
| Pre-obesity (overweight) | 23.0 – 24.9 | 70.4 – 76.3kg |
| Obesity class I | 25.0 – 29.9 | 76.6 – 91.6kg |
| Obesity class II | 30.0 – 34.9 | 91.9 – 106.9kg |
| Obesity class III | 35.0+ | 107.2kg+ |
Waist catches what BMI misses
BMI cannot tell muscle from fat, so abdominal obesity is assessed separately. The KDCA thresholds are 90cm for men and 85cm for women.
The women's figure is 85cm rather than 80cm for a reason: before 2006 it was 80cm, but that sat so close to the Korean female average that it stopped discriminating usefully, and it was revised upward.
The example above (92cm waist) is obese by BMI and abdominally obese by waist. The harder and more common case is a normal BMI with a large waist — covered separately in normal BMI but a belly.
Where the daily calorie figure comes from
Basal metabolic rate here uses the Mifflin-St Jeor equation:
- Men — 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
- Women — 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
For the example: 10×78 + 6.25×175 − 5×35 + 5 = 1,704 kcal. Multiply by an activity factor for the daily figure.
| Activity level | Factor | At 1,704 kcal |
|---|---|---|
| Sedentary | 1.2 | 2,045 kcal |
| Lightly active (1–3 sessions a week) | 1.375 | 2,343 kcal |
| Moderately active (3–5) | 1.55 | 2,641 kcal |
| Very active (6–7) | 1.725 | 2,939 kcal |
| Extra active (physical job, twice daily) | 1.9 | 3,238 kcal |
This equation could not be found in any Korean public-agency document. Neither Mifflin-St Jeor nor Harris-Benedict appears in KDCA or Ministry of Health and Welfare material. It is widely used internationally, but it is not a government-endorsed formula, and this article says so rather than implying otherwise.
What Korea does publish is estimated energy requirement by sex and age, in the 2020 Dietary Reference Intakes for Koreans:
| Age | Men (kcal/day) | Women (kcal/day) |
|---|---|---|
| 19–29 | 2,600 | 2,000 |
| 30–49 | 2,500 | 1,900 |
| 50–64 | 2,200 | 1,700 |
| 65–74 | 2,000 | 1,600 |
The calculator's 2,343 kcal sits a little below the 2,500 kcal reference for that age band. The reference assumes population-average height and weight at a moderate activity level, so a figure built from one person's measurements is expected to differ. A gap between the two does not make either one wrong.
The −500 kcal on the weight-loss row follows the KDCA's guidance that a 500 kcal daily deficit corresponds to about 0.5 kg a week. Note that the widely quoted “1 kg = 7,700 kcal” conversion is deliberately not used here — no Korean public-agency source stating that figure could be found. Why progress stalls is covered in why eating less stops working.
“Ten thousand steps” is not a standard
On the spending side of the equation, the number everyone repeats is 10,000 steps a day.
Checked against the sources, Korean public health bodies do not use it. The KDCA states plainly that there is “no absolute standard for walking time or step count”, and instead suggests starting at 30 minutes, three or four times a week.
The official guidance is written in minutes, not steps:
| Item | Adults aged 19–64 |
|---|---|
| Moderate-intensity aerobic | 150–300 minutes a week |
| Vigorous-intensity aerobic | 75–150 minutes a week (may be combined with moderate) |
| Strength training | 2 or more days a week (8–12 repetitions per set) |
“Moderate” is defined too. The KDCA describes it as 3.0–5.9 times resting energy expenditure, with the heart beating a little faster and breathing slightly harder. The familiar “you can talk but not sing” phrasing is not used here, because it could not be found in any Korean public-agency text.
For what it is worth, the 10,000 figure is generally traced to a 1965 Japanese pedometer sold as the “manpo-kei” — literally “ten-thousand-step meter”. That origin was only confirmed in press coverage, not in a primary academic source.
The practical conclusion is simple. Missing 10,000 is not failure. Someone who barely walks adding two or three thousand steps beats aiming at ten thousand and quitting on day three. Indoor options are in quiet home cardio, and leg strength in the lower-body routine.
What this calculator does not account for
- Body fat percentage and muscle mass — BMI sees only weight. Muscular people read high; people with little muscle can read normal while carrying high body fat.
- Pregnancy and breastfeeding, adolescents, older adults — adult BMI thresholds do not transfer directly to these groups.
- Individual variation in metabolism — identical inputs, different real-world burn. The equation fits an average.
- Illness and medication — thyroid conditions in particular move metabolic rate directly. Signals are in what a thyroid signals.
- Calories per kilogram of body weight — omitted, as explained above, for lack of a verifiable source.
Questions that remain
Are the six rows on screen all the same kind of number?
No. The top three — BMI 25.5, obesity class I, and the 56.7–70.1 kg healthy range — come from published standards. The bottom three — a BMR of 1,704 kcal, daily maintenance of 2,343 kcal and the 1,843 kcal weight-loss target — come from an equation fitted to population data. It is exactly half and half. They sit side by side, but the top three give the same answer for anyone of that height and weight, while the bottom three can be meaningfully off for an individual, because the equation cannot see muscle or body fat.
English-language sources call a BMI of 25.5 overweight. Why does this say obesity?
Two different scales. The WHO puts overweight at 25 and obesity at 30; the Korean scale used by the KDCA and the Korean Society for the Study of Obesity puts them at 23 and 25. The two thresholds did not move down by the same amount — overweight is 2 lower, obesity 5 lower. That is why the same 25.5 reads as overweight on the WHO scale and obesity class I on the Korean one. The thresholds were lowered because Asian populations tend to carry more body fat at a given BMI and meet metabolic risk earlier.
Is the 85cm waist threshold for women more lenient than the 90cm for men?
It is a revised figure rather than a lenient one. Before 2006 it was 80cm, but that sat so close to the Korean female average that it stopped separating anyone usefully, so it was moved up. The current KDCA thresholds are 90cm for men and 85cm for women. Waist is measured separately precisely because BMI cannot tell muscle from fat — the two are meant to be read together.
The calculator says 2,343 kcal but the national reference table says 2,500. Which is right?
Neither is wrong. The 2,500 kcal figure for men aged 30–49 in the 2020 Dietary Reference Intakes for Koreans assumes population-average height and weight at a moderate activity level. The 2,343 kcal is built from one person's height, weight, age and activity setting. Different assumptions, so a gap is expected. Do keep in mind that the calculator's side rests on an estimating equation — one that could not be found in any Korean public-agency document.
Why is the familiar “1 kg = 7,700 kcal” conversion missing here?
Because no Korean public-agency source stating it could be found, so it was left out on purpose. The −500 kcal on the weight-loss row comes instead from the KDCA's guidance that eating 500 kcal less a day corresponds to about 0.5 kg a week. The same rule kept out “10,000 steps a day” and the “you can talk but not sing” description of moderate intensity. On walking, the KDCA states plainly that there is no absolute standard for time or step count.
Sources and where to verify
- KDCA national health information portal — obesity (BMI 25+ is obesity; classes I–III; abdominal obesity at 90cm men / 85cm women)
- Korean Society for the Study of Obesity — diagnosis of obesity (WHO 25/30 against Asia-Pacific and KSSO 23/25)
- KDCA national health information portal — physical activity (150–300 min moderate, 75–150 min vigorous, strength 2+ days, moderate = 3.0–5.9 METs)
- KDCA national health information portal — knee osteoarthritis and walking (“there is no absolute standard for walking time or step count”)
- Ministry of Health and Welfare · Korean Nutrition Society — 2020 Dietary Reference Intakes for Koreans (estimated energy requirement by sex and age)
Written as of July 2026. The BMI thresholds, waist thresholds and activity guidance are transcribed from the sources above, and the on-screen values were reconciled against an independent calculation before the screenshot was taken. The basal metabolic rate equation is an internationally used estimate that could not be found in any Korean public-agency document; the “1 kg = 7,700 kcal” conversion and the “talk but not sing” description of moderate intensity were both left out for the same reason. This is general health information and does not replace a diagnosis. If you have a condition or need to change your weight, speak to a clinician before starting.
