Is BMI 25.5 Obese or Overweight? Korea's Scale vs the WHO's

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.

Which is why a BMI number means nothing without saying whose scale you read it on. The calculator below judges on the Korean scale used by the Korean Society for the Study of Obesity and the KDCA, and if you add your waist measurement it checks abdominal obesity too.

What the five 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 two rows are values written in 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.

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.