What Is a Healthy BMI? How to Calculate It and What It Can't Tell You
Body mass index is the most widely used screening number for weight. It's quick and useful at the population level — and it has blind spots worth knowing.
The formula
BMI = weight (kg) ÷ height (m)². In pounds and inches: 703 × weight (lb) ÷ height (in)².
Example: 80 kg and 1.75 m → 80 ÷ 3.0625 = 26.1.
WHO categories for adults
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5–24.9 | Healthy weight |
| 25–29.9 | Overweight |
| 30 and above | Obesity (classes I, II, III from 30, 35, 40) |
Some countries use lower cut-offs for Asian populations, because health risks rise at lower BMI.
Healthy range for your height
Reverse the formula: weight = BMI × height². At 1.75 m, BMI 18.5–24.9 corresponds to about 56.7–76.3 kg. The BMI calculator shows your range in kg or lb.
What BMI doesn't tell you
- Muscle vs fat: muscular people can have a "high" BMI without excess fat.
- Where fat is: fat around the waist carries more risk than fat elsewhere. The waist-to-height ratio is a simple complement.
- Children and teens: they need age- and sex-specific growth charts, not adult cut-offs.
- Pregnancy and older adults: interpret with a professional.
Use BMI as a starting point for a conversation with a doctor, not as a diagnosis.
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