Visual gauge with age and gender-adjusted interpretation. Understand what your BMI means — and when it doesn't tell the full story.
BMI (Body Mass Index) divides your weight by height squared. A normal BMI is 18.5-24.9 per WHO. Enter your height and weight above for an instant visual result with clinical interpretation.
Written by Ash K · Last updated: June 2026 · Sources cited below
BMI (Body Mass Index) is your weight in kilograms divided by your height in meters squared. It's the most widely used screening tool for weight classification — and also the most widely misunderstood. A BMI of 25 does not mean you're unhealthy. It means your weight-to-height ratio falls into the "overweight" category by WHO standards.
This calculator gives you your BMI and WHO classification. It also tells you the limitations — because those matter as much as the number.
WHO BMI Classification Scale
Key Takeaway: BMI = weight (kg) ÷ height (m²). It's a ratio, not a health assessment. WHO categories: below 18.5 = underweight, 18.5–24.9 = normal, 25–29.9 = overweight, 30+ = obese. BMI cannot distinguish muscle from fat — a muscular athlete and a sedentary person can have identical BMIs with very different health profiles.
| BMI Range | WHO Classification | Context |
|---|---|---|
| Below 16 | Severe underweight | Medical evaluation recommended |
| 16–16.9 | Moderate underweight | Nutritional assessment recommended |
| 17–18.4 | Mild underweight | Monitor; may be normal for some |
| 18.5–24.9 | Normal weight | Reference range for most adults |
| 25–29.9 | Overweight | Evaluate body composition, not just BMI |
| 30–34.9 | Obese Class I | Health risk increases statistically |
| 35–39.9 | Obese Class II | Significant health risk increase |
| 40+ | Obese Class III | Highest risk category |
BMI does not measure body fat. It measures weight relative to height. A 5'10" man weighing 200 lbs has a BMI of 28.7 ("overweight") whether he's a bodybuilder at 12% body fat or sedentary at 35% body fat. For actual body composition, use our body fat calculator.
BMI doesn't account for muscle mass. Muscle is denser than fat. Athletes, weightlifters, and physically active people routinely score "overweight" by BMI while being metabolically healthy.
BMI varies by ethnicity. Research shows that health risks associated with specific BMI values differ across ethnic groups. Some Asian populations experience diabetes risk at BMI 23 (within the "normal" range), while some Pacific Islander populations maintain health at BMI 27–28.
Note: Despite its limitations, BMI remains useful as a population-level screening tool. At the extremes (BMI below 16 or above 35), it reliably identifies elevated health risk. In the middle ranges (25–30), individual assessment of body composition, fitness, and metabolic markers is more informative than BMI alone.
Metric: BMI = weight (kg) ÷ height (m)²
Example: 75 kg, 1.75 m → 75 ÷ 3.0625 = 24.5
Imperial: BMI = (weight (lbs) × 703) ÷ height (inches)²
Example: 165 lbs, 5'9" (69 in) → (165 × 703) ÷ 4761 = 24.4
Tip: Your BMI is one data point. Combine it with waist-to-hip ratio (fat distribution), body fat percentage (composition), and basic metabolic markers (blood pressure, blood sugar, cholesterol) for a genuinely useful health snapshot. No single metric is sufficient.
For teenagers, adult BMI categories don't apply — use our BMI calculator for teens which uses CDC age-specific percentiles.
Bottom Line: BMI is a screening tool, not a health diagnosis. It's most useful at the extremes and least useful for athletes, muscular individuals, and anyone whose weight doesn't reflect their body composition. Know your number, understand its limitations, and use it alongside — not instead of — body composition metrics.
When BMI Gets It Wrong — Same BMI, Different Bodies
What is a healthy BMI?
WHO classifies BMI 18.5–24.9 as "normal weight." But health depends on more than BMI — body composition, fitness, metabolic markers, and lifestyle factors all matter. A BMI of 26 with excellent fitness and metabolic health may be healthier than a BMI of 22 with poor fitness.
How accurate is BMI?
For population-level screening, BMI is reasonably useful. For individuals — particularly athletes, older adults, and those with high or low muscle mass — it can be misleading. It's a ratio, not a measurement of health.
What BMI is considered obese?
BMI 30 or above is classified as obese by WHO standards. Class I: 30–34.9. Class II: 35–39.9. Class III: 40+.
This tool is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult your healthcare provider with questions about your health.