Guide
Understanding BMI
What Body Mass Index measures, how categories work, and why BMI is only one piece of a health picture.
BMI is a simple ratio of weight to height used as a broad screening metric for adults. It is easy to calculate and widely referenced — and widely misunderstood.
What BMI is good for
- Population-level and clinical screening
- Quick context alongside other vitals
- Tracking change over time for the same person
What BMI is not
- A direct measure of body fat
- A diagnosis of health or fitness
- Equally accurate for every body composition (for example high-muscle athletes)
Categories (adult WHO ranges)
Rough adult bands include underweight, normal weight, overweight, and obesity classes. Children’s categories use percentiles instead of adult cutoffs.
Next steps on Calcuit
- Run your numbers in the BMI Calculator.
- Pair with Body Fat estimates when measurement quality allows.
- For energy targets, see Calorie or TDEE.
Always discuss medical concerns with a clinician — online estimates are not care.
References
Sources consulted while preparing this article. Links may lead to third-party sites.
- BMI Calculator — Calculator.netAdult BMI categories and formula overview.
- WHO — Body mass indexPopulation health context for BMI cutoffs.