What BMI Measures
Body Mass Index (BMI) is a simple ratio of weight to height: weight (kg) divided by height (m) squared. It’s fast to compute and useful for population-level trends, which is why many guidelines and studies reference it.
Calculate yours instantly with our
BMI Calculator (metric or US units).
Common BMI Categories
| BMI | Category |
|---|
| < 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0+ | Obesity (Class I/II/III) |
Ranges vary slightly by organization and age group. Always consult a licensed professional for personalized guidance.
What BMI Misses
- Body composition: BMI doesn’t separate fat from muscle. Athletes can score “overweight” despite low body fat.
- Fat distribution: Visceral fat around the abdomen is riskier than subcutaneous fat; BMI can’t tell the difference.
- Age and sex differences: Two people with the same BMI can have very different health profiles.
- Ethnic population differences: Some groups experience health risks at lower BMI thresholds.
Complement BMI with These Metrics
- Waist circumference: A practical proxy for visceral fat. Track changes over time.
- Body fat percentage: From calipers to bioimpedance to DEXA scans (each with pros/cons).
- Fitness markers: Resting heart rate, VO2 max estimates, strength and mobility tests.
- Lab work & history: Lipids, A1C, blood pressure, family history, medications.
How to Use Our BMI Calculator
- Open the BMI Calculator.
- Choose US or metric units, enter height and weight, and hit “Calculate.”
- Review the result and category. Add waist and body fat metrics for context.
Healthy, Sustainable Changes
Small habits matter more than perfection: consistent activity, balanced meals, sufficient sleep, and stress management. Rapid “fixes” rarely last; gradual progress does.
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