Enter your height, weight, age and sex to get your BMI and weight category, plus your basal metabolic rate (BMR) and estimated daily calorie needs by activity level.
Daily calorie needs are estimated by multiplying BMR by an activity factor. BMI doesn't account for muscle mass, so muscular or very athletic bodies may score higher than their body-fat percentage would suggest — treat it as a general screening number, not a diagnosis.
Body Mass Index is your weight divided by the square of your height. It was devised in the 1830s by the Belgian statistician Adolphe Quetelet to describe the physique of the "average man" across a population, which is why it was originally called the Quetelet Index.
That origin matters. BMI was built to describe groups, not to diagnose individuals, and it still behaves that way. Across a population it estimates obesity prevalence cheaply and quickly; for one person it is closer to a first-pass screening signal that tells you whether to look further.
BMI = weight (kg) ÷ height (m)². Height goes in as metres, not centimetres, and it is squared.
At 175 cm and 70 kg: 1.75 × 1.75 = 3.0625, and 70 ÷ 3.0625 = 22.86. If a calculator disagrees with that arithmetic, the usual cause is height entered in centimetres or a mix of pounds and inches.
In imperial units the formula is BMI = 703 × weight (lb) ÷ height (in)². The 703 is only a unit-conversion constant, not a different method.
The WHO international bands are: under 18.5 underweight, 18.5–24.9 normal, 25–29.9 overweight, and 30 or above obese, with obesity split into 30–34.9 (class I), 35–39.9 (class II) and 40+ (class III).
Body-fat percentage at a given BMI differs between populations, though. East Asian populations carry more fat, and more of it abdominally, at the same index — so the WHO Western Pacific cut-offs treat 23 and above as overweight and 25 and above as obese. Korean clinical practice generally follows those.
That means "BMI 24" has no fixed meaning until you say which standard you are using: normal under the international bands, overweight under the Asian ones. When another calculator disagrees with this one, this is usually why.
It cannot separate muscle from fat. Because it uses one weight figure, a muscular person lands in the overweight or obese band despite a low body-fat percentage. Athletes are misclassified this way routinely.
It does not know where the fat sits. At the same BMI, visceral (abdominal) fat carries a markedly higher metabolic risk than subcutaneous fat, which is why waist circumference or waist-to-hip ratio is recommended alongside it.
It ignores age and sex. Body composition shifts with age — less muscle, more fat at the same weight — while the index stays put. Women generally carry a higher body-fat percentage at the same BMI.
It is an adult measure. Children and adolescents are assessed against age- and sex-specific growth percentiles, and the adult bands are not applied during pregnancy.
Basal metabolic rate is the energy your body spends keeping itself alive at complete rest. It accounts for roughly 60–70% of daily expenditure in most adults.
Multiply it by an activity factor and you get total daily energy expenditure. The common factors are 1.2 for sedentary, 1.375 for light exercise one to three days a week, 1.55 for moderate exercise three to five days, 1.725 for hard exercise six or seven days, and 1.9 for physical work or two sessions a day.
Those steps are coarse because there is no evidence supporting finer ones, not because the coarseness is a simplification. Two people who both "train three times a week" can differ substantially, so treat the number as a starting point and adjust it against two or three weeks of actual weight change.
A kilogram of body fat corresponds to roughly 7,700 kcal. Eating 500 kcal a day less works out arithmetically to about 0.45 kg a week.
A daily deficit of 300–500 kcal is the usual recommendation because that range tends to cost less muscle and provoke less metabolic adaptation. Larger deficits lose weight faster at first and are adhered to less often.
Eating below your basal metabolic rate is not advised. For gaining, the mirror-image approach — a surplus of 200–300 kcal a day paired with resistance training — adds less fat than a larger one.
Waist circumference directly captures the abdominal fat BMI misses. Body-fat percentage can be estimated with bioelectrical impedance scales or skinfold calipers.
Blood pressure, fasting glucose, and a lipid panel (total cholesterol, HDL, triglycerides) can be abnormal at a normal BMI and normal at a high one. If you have recent bloodwork, that combination tells you far more than the single index does.
A BMI of 30 or above, or below 18.5; a large unplanned change in weight over a few months; or an existing obesity-related diagnosis (type 2 diabetes, hypertension, sleep apnoea, fatty liver disease) are all reasons to get assessed regardless of what this page says.
This calculator does not replace that assessment. At the point where a judgement is needed, you want someone looking at your test results and history together.
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). This calculator reads the result against the WHO Western Pacific (Asia-Pacific) cut-offs — 18.5–22.9 normal, 23–24.9 pre-obese, 25 and above obese — because that is what clinics across East Asia use. The WHO international bands put the healthy range at 18.5–24.9 instead; the guide below compares the two.
Basal Metabolic Rate is the number of calories your body burns at rest to keep basic functions running. It's the starting point for estimating your daily calorie needs.
BMI is a quick screening tool, not a diagnosis. It doesn't distinguish muscle from fat, so athletes and some body types may fall outside the usual ranges.
Trimming roughly 300–500 kcal below your daily calorie needs (maintenance) is a common, sustainable target for gradual weight loss.
East Asian populations carry more body fat at the same BMI, so the WHO Western Pacific cut-offs (23 overweight, 25 obese) are widely used across Korea, Japan and China — about 2–5 points lower than the international 25/30 thresholds.
What this tool bases its numbers on, and how far those numbers go.
BMI = weight (kg) ÷ height (m)². BMR uses the Mifflin-St Jeor equation; daily calories are BMR × an activity factor (1.2–1.9).70 kg ÷ (1.75 m × 1.75 m) = BMI 22.86