Core answer: BMI = weight(kg) ÷ height(m)². 1.70m, 70kg: 70 ÷ 2.89 ≈ 24.2 — the upper edge of China's normal range (18.5-23.9), tipping into overweight.
How to compute BMI
Two inputs only — weight and height. The formula is fixed with no age or sex correction for adults.
BMI = weight(kg) ÷ height(m)²
Example: 1.70m, 70kg → 70 ÷ (1.70 × 1.70) = 70 ÷ 2.89 ≈ 24.2 → overweight band (24-27.9) on the Chinese scale. Same height at 60kg → BMI ≈ 20.8 → normal.
What counts as normal (Chinese standard)
China's WS/T 428 industry standard splits adult BMI into four bands. Normal is 18.5-23.9; both ends carry risk.
| Band | BMI range | Reference |
|---|---|---|
| Underweight | < 18.5 | Higher osteoporosis and immunity risks |
| Normal | 18.5-23.9 | Healthy weight range |
| Overweight | 24-27.9 | Chronic-disease risk rising; watch waistline |
| Obese | ≥ 28 | Markedly higher hypertension/diabetes/CVD risk |
23.9 is the ceiling of "normal" in China — 24 is overweight. The line is lower than most people assume.
Healthy weight range: 18.5 × height(m)² to 23.9 × height(m)².
Add the waistline check: men < 85cm, women < 80cm; beyond that signals excess abdominal fat.
Scope: adults 18+ only. Children, pregnant/breastfeeding women and the elderly need dedicated standards.
Chinese vs WHO standards
The same person can be "overweight" in China and "normal" by WHO — not an error, just different populations and data.
| Band | China (WS/T 428) | WHO |
|---|---|---|
| Underweight | < 18.5 | < 18.5 |
| Normal | 18.5-23.9 | 18.5-24.9 |
| Overweight | 24-27.9 | 25-29.9 |
| Obese | ≥ 28 | ≥ 30 |
Why: WHO's bands were built on European/North American data. Asian epidemiology later showed that at the same BMI, Asians carry 3-5pp more body fat, and diabetes/cardiovascular risk rises at lower BMI.
Which to use: in China, hospitals and checkups use WS/T 428. WHO's scale is for international comparison and research. For daily health management in China, follow the Chinese standard.
What is my healthy weight?
Invert the normal-BMI band back into weight: multiply height² by 18.5 and 23.9.
Lower bound = 18.5 × height(m)²; upper bound = 23.9 × height(m)²
| Height | Lower (kg) | Upper (kg) | Span |
|---|---|---|---|
| 1.55m | ~44.4 | ~57.4 | ~13kg |
| 1.60m | ~47.4 | ~61.1 | ~14kg |
| 1.65m | ~50.3 | ~65.0 | ~15kg |
| 1.70m | ~53.5 | ~69.1 | ~16kg |
| 1.75m | ~56.7 | ~73.1 | ~16kg |
| 1.80m | ~59.9 | ~77.4 | ~17kg |
At 1.70m the healthy span is ~53.5-69.1kg — nearly 16kg wide. No need to chase one magic number: inside the band with body fat and waistline in range is healthy.
BMI's limits
BMI is a screening tool, not a diagnosis. For these groups it misreads:
- Muscular people (athletes, lifters): muscle outweighs fat; BMI may read overweight or obese while body fat is low and metabolic health excellent.
- Apple-shaped bodies: normal BMI but waist over the line (men ≥ 85cm / women ≥ 80cm) — visceral fat risk gets underestimated.
- Pregnant women: pregnancy gain is normal physiology; adult BMI does not apply.
- Children/teens: use age-specific BMI percentiles.
- Adults 65+: muscle loss and lower bone density mean more fat at the same BMI.
Complementary metrics:
- Body fat %: reference 10-20% men, 18-28% women — a truer fat gauge than BMI.
- Waist circumference: men < 85cm, women < 80cm — directly tied to visceral fat.
- Waist-to-hip ratio: ideally < 0.9 men, < 0.85 women — where the fat sits.
BMI measures weight against height; the waist measures where fat hides. Use both rulers for a complete picture.