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BMI Calculator

Calculate BMI from height and weight, classified by the Chinese standard WS/T 428-2013, with a healthy weight range. Metric and imperial units supported.

Height and weight go in and BMI comes out — but fewer people know that the overweight line used for Chinese populations (WS/T 428-2013) is stricter than the international one: 24 rather than 25. This tool classifies against that health-industry standard and gives the healthy weight range for your height at the same time, so "how many kilos should go" has a definite anchor. Anyone carrying a lot of muscle should read the note below.

Why the Chinese standard rather than the WHO one: metabolic problems appear at a lower BMI in Chinese populations — the overweight line is 24 against the WHO's 25, and the obesity line 28 against 30. One caveat: BMI does not separate muscle from fat, so a heavily muscled person can be misclassified as overweight, and body-fat percentage is the better reading in that case.

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How to use

  1. Enter height and weight, in metric or imperial units.
  2. Read the BMI and its category against the Chinese standard.
  3. Check the healthy weight range for your height.
  4. Use body-fat percentage instead if you carry a lot of muscle.

How it works

The BMI formula

Formula: BMI = weight (kg) / height (m)^2. For example 170 cm and 65 kg: 65 / 1.70^2 = 65 / 2.89 = 22.5.

China's BMI classification

China's standard (WS/T 428-2013) classification: BMI < 18.5 is underweight, 18.5-23.9 normal, 24-27.9 overweight, and 28 or above obese.

How to compute the healthy weight range

The healthy weight range is back-solved: weight = BMI x height (m)^2. At 170 cm, a normal BMI maps to 53.5-69.1 kg.

Calculation basis: the BMI categories of China's health standard WS/T 428-2013 (18.5 / 24 / 28 cut-offs). For adults only, and not a substitute for medical diagnosis.

Code example

JavaScript BMI and the Chinese-standard bands 

function bmi(hCm, wKg) {
  const v = wKg / (hCm / 100) ** 2;
  const level = v < 18.5 ? "underweight" : v < 24 ? "normal"
    : v < 28 ? "overweight" : "obese";               // WS/T 428-2013
  const lo = (18.5 * (hCm / 100) ** 2).toFixed(1);
  const hi = (23.9 * (hCm / 100) ** 2).toFixed(1);
  return { bmi: v.toFixed(1), level, healthyRange: lo + "~" + hi + "kg" };
}

bmi(170, 65);   // 22.5 normal, healthy weight 53.5~69.1kg

Python The same formulas in Python 

def bmi(h_cm, w_kg):
    v = w_kg / (h_cm / 100) ** 2
    level = ("underweight" if v < 18.5 else "normal" if v < 24
             else "overweight" if v < 28 else "obese")
    return round(v, 1), level

bmi(170, 65)   # (22.5, "normal")

# Chinese standard: 24 overweight / 28 obese (WHO uses 25/30 — do not mix the two)

FAQ

How does China's standard differ from WHO's?

WHO uses 25 as the overweight and 30 as the obesity cutoff; China's is stricter at 24 and 28. This is because Chinese people have a higher body-fat percentage and greater health risk at the same BMI, so lower cutoffs apply. This tool classifies by China's standard.

Is BMI accurate? What about muscular people?

BMI looks only at height and weight, not distinguishing muscle from fat, so gym-goers and athletes often show a high BMI without being obese. Judge together with waist circumference (men < 85 cm, women < 80 cm) and body-fat percentage.

Do children and teens use this BMI standard?

No. Minors should be assessed by age- and sex-specific BMI percentile curves (growth charts); under 18, consult a pediatrician or use a dedicated child growth standard.

What is the BMI formula?

BMI = weight (kg) / height (m)^2. For example 65 / 1.70^2 = 22.5. In centimeters, divide by 100 first to get meters; the imperial formula is BMI = 703 x weight (lb) / height (in)^2.

Is BMI appropriate during pregnancy or breastfeeding?

No. Pregnancy weight includes the fetus, amniotic fluid and increased blood volume, so BMI runs clearly high and can't be judged by the ordinary adult standard. Only pre-pregnancy BMI is meaningful; pregnancy weight gain should follow the obstetrician's recommended range.

How much weight loss counts as effective?

Generally a clinically meaningful target is "losing 5-10% of body weight and sustaining it." For overweight people, a 5% loss improves blood pressure, blood sugar and lipids. A weekly loss of 0.5-1 kg is advisable; faster loss is mostly water and rebounds easily.

Does height varying between morning and evening affect BMI?

Slightly. Height can differ by 1-2 cm within a day, making BMI differ by about 0.1-0.3 — normal fluctuation. Measure at a fixed time (like on waking) so comparisons are meaningful.

Are my height and weight recorded or uploaded?

No. Height and weight are used in a single division in your browser, not sent to a server, and we have no collection endpoint; the result appears only on the page. If you used "history," records are stored in local browser storage (localStorage), erasable with "clear," and gone on close in incognito mode.