BMI Calculator
A weight-to-height ratio used worldwide to classify body weight. Simple, fast, and validated across large populations — but best interpreted alongside other measurements.
Your Measurements
Used to refine the interpretation for older adults.
Your Result
Enter your weight and height, then click Calculate.
📋 What Your Result Means
For educational purposes only — not medical advice.
The gauge above shows where your result sits. Use the standard WHO classification table below, then read the important caveats that follow.
| Category | BMI Range | Health Risk |
|---|---|---|
| Underweight | < 18.5 | Increased |
| Normal weight | 18.5 – 24.9 | Low |
| Overweight | 25 – 29.9 | Moderate |
| Obese Class I | 30 – 34.9 | High |
| Obese Class II | 35 – 39.9 | Very High |
| Obese Class III | ≥ 40 | Extremely High |
Ethnic-specific cutoffs: The WHO recommends lower thresholds for Asian populations (South Asian, Chinese, Japanese): overweight begins at BMI 23 and obesity at BMI 27.5, due to higher metabolic risk at lower body weights (WHO Expert Consultation, 2004).
The J-curve and optimal range: A large meta-analysis of 97 studies (2.88 million individuals) found that the lowest all-cause mortality occurs at a BMI of approximately 22 to 25. Overweight (BMI 25-30) showed no significant excess mortality, but obesity (BMI 30+) was clearly associated with higher mortality (Flegal et al. 2013, JAMA; DOI: 10.1001/jama.2012.113905).
When to ignore BMI: BMI systematically misclassifies muscular individuals as overweight or obese because it cannot distinguish fat from lean tissue. If you strength train regularly, use the FFMI calculator instead. BMI also underestimates adiposity in older adults who have lost muscle (sarcopenia) and in sedentary individuals with normal weight but high body fat ("skinny fat"). Always pair BMI with at least one other metric such as waist circumference, body fat percentage, or waist-to-hip ratio for a reliable picture.
BMI = weight (kg) ÷ height (m)²
Limitations
BMI does not distinguish between fat mass and lean mass. It may misclassify muscular individuals as overweight, and may underestimate adiposity in older adults who have lost muscle. It was primarily derived from European populations and may not be equally applicable across all ethnicities.
✓ Strong EvidenceWant to learn more? Read our in-depth article: Is BMI Actually a Good Measure of Health? →
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