BMI in 30 seconds
BMI is a simple ratio of your weight to your height squared. It doesn't measure fat directly — but for a population, it correlates well enough with health risk that doctors use it as a quick screening tool.
- Under 18.5 — Underweight
- 18.5 – 24.9 — Normal weight
- 25 – 29.9 — Overweight
- 30+ — Obese (Class I, II, or III depending on severity)
BMI has real limits — read this
BMI doesn't distinguish muscle from fat. A muscular athlete may score "overweight" with very low body fat. A sedentary person may score "normal" with concerning fat percentage. Use BMI as one signal among many — waist circumference and metabolic blood markers are often more informative.
Better metrics if you want them
Waist-to-height ratio: keep it under 0.5 regardless of age, sex, or BMI. A 30-second tape measurement that often beats BMI for predicting metabolic risk.
FAQ
- Is BMI accurate for athletes? Not really — muscle weight inflates the number. Use body fat percentage instead.
- Does it differ by sex or ethnicity? Yes — research shows Asian populations may face increased metabolic risk at lower BMI values. WHO has proposed lower cutoffs (23 for overweight) for Asian populations.
- Is my data sent anywhere? No. Everything is calculated locally in your browser.