Understanding Your BMI Score
What is BMI?
Body Mass Index (BMI) is a number calculated from your height and weight. It was developed in the 1830s by Belgian mathematician Adolphe Quetelet as a simple way to classify body weight relative to height.
The formula:
BMI = weight (kg) ÷ height² (m²)
Or in imperial units: BMI = (weight in lbs × 703) ÷ height² (in²)
The standard BMI ranges
| BMI | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
These ranges were established by the World Health Organization and are widely used by healthcare providers for initial screening.
What BMI tells you
BMI gives a rough snapshot of whether your weight is in a healthy range for your height. It's useful because it's:
- Fast to calculate — you only need two numbers
- Comparable — consistent across populations for large studies
- Free — no equipment, no lab work
For population-level health research, BMI works well. For an individual, it's a starting point — not a verdict.
What BMI doesn't tell you
This is the important part. BMI has real limitations:
It doesn't distinguish fat from muscle. A heavily muscled athlete may have a BMI in the "overweight" range while carrying very little body fat. A sedentary person can have a "normal" BMI with unhealthy fat distribution.
It doesn't account for where fat is stored. Belly fat (visceral fat) is more dangerous than fat stored around the hips or thighs. BMI can't tell the difference.
It varies by age and sex. Older adults naturally carry more body fat. Women generally carry more fat than men at the same BMI. The standard ranges don't fully account for this.
It varies by ethnicity. Research suggests that health risks associated with higher body fat begin at lower BMI values in some populations (particularly South and East Asian adults).
A more complete picture
If you want a better understanding of your health, consider pairing BMI with:
- Waist circumference — a waist over 88 cm (35 in) for women or 102 cm (40 in) for men suggests higher cardiovascular risk
- Waist-to-height ratio — aim for less than 0.5 (your waist should be less than half your height)
- Body fat percentage — measured with calipers, DEXA scan, or bioimpedance
- Blood markers — cholesterol, blood pressure, fasting glucose
Ideal weight range
The "ideal weight" for a given height is typically the weight range that keeps BMI between 18.5 and 24.9. For a 170 cm person, that's roughly 53–72 kg. The Good Patrone BMI calculator shows this range automatically.
Final thought
BMI is a useful screening tool, not a diagnosis. If your BMI is outside the normal range, it's a reason to talk to a doctor — not a reason to panic. Context, habits, and overall health markers matter far more than a single number.
Use it as one data point among many, and don't let it define how you feel about your body.