What Is BMI? How to Understand Body Mass Index
Learn what BMI is, how it is calculated, what the categories mean, and why it is just one piece of the health puzzle.
Guide overview
Body Mass Index (BMI) is the most widely used screening tool for healthy weight. But what does your number actually mean?
Learn what BMI is, how it is calculated, what the categories mean, and why it is just one piece of the health puzzle.
Key points from the source guide
The source guide defines BMI as weight in kilograms divided by height in meters squared.
It summarizes common BMI categories and explains why BMI is a screening tool rather than a diagnosis.
It recommends pairing BMI with body fat and waist measurements when body composition matters.
Try the related Toolars calculators
This migrated guide links to these Toolars tools: bmi-calculator, body-fat-calculator.
Tools mentioned in this article
Frequently asked questions
- Is BMI accurate for everyone?
- No. BMI is a population-level screening tool, not a perfect individual metric. It may overestimate body fat in muscular individuals and underestimate it in elderly people who have lost muscle mass.
- What BMI is considered obese?
- According to WHO standards: BMI 25-29.9 is overweight, 30-34.9 is Class I obesity, 35-39.9 is Class II obesity, and 40+ is Class III obesity. Asian populations may use lower thresholds.