Understanding BMI and Its Limits
BMI is a quick screening number that compares your weight to your height. It is not a diagnosis, and it does not describe body composition — but used correctly it is still a useful starting point.
What BMI is
BMI stands for Body Mass Index. It is calculated by dividing weight in kilograms by height in metres squared (kg/m²).
The result is compared against fixed ranges: underweight, normal, overweight, and obese. These ranges were derived from large adult populations and are used for public-health screening.
The standard ranges
- Under 18.5 — underweight
- 18.5 to 24.9 — normal
- 25 to 29.9 — overweight
- 30 and above — obese
Where BMI falls short
BMI cannot tell muscle apart from fat. Athletes and heavily muscled people often score as overweight despite having very low body fat.
It also ignores fat distribution, bone density, age, gender, and ethnicity — all of which change health risk at the same BMI number.
- Muscular adults may score high without excess fat.
- Older adults may score normal while carrying unhealthy visceral fat.
- Children and pregnant people need different scales entirely.
How to use BMI sensibly
Treat BMI as one signal among several. Waist circumference, resting heart rate, blood pressure, and how you feel day to day matter more than a single number.