BMI Calculator
Calculate your Body Mass Index in metric or imperial units. See what the number means and where you land on the WHO scale.
BMI is a screening tool, not a diagnosis. It does not distinguish muscle from fat and has known limitations for athletes, older adults, and some ethnic groups.
What BMI measures (and what it doesn't)
Body Mass Index is weight divided by height squared. It was designed in the 1830s as a statistical tool for studying populations — not as an individual diagnostic. It correlates with body fat across a large sample, but for any given person it can be misleading, especially at the extremes of muscle mass or bone density.
How to interpret your number
Use BMI as one data point, not a verdict. If your BMI is in the healthy range (18.5–24.9) and you feel well, that's a good sign. If it's outside that range, check whether you carry more muscle than average (common for strength athletes) or whether you've had recent unexplained weight changes. Persistent out-of-range BMI combined with other signals (fatigue, blood pressure, waist measurement > 40" for men or 35" for women) deserves a conversation with a doctor.
The healthy weight range shown
For your height, this calculator shows the weight range that would put your BMI between 18.5 and 25. This is the "normal" range per WHO; it does not mean you must weigh within it to be healthy, only that populations in this range tend to have the lowest mortality from chronic disease.
Better measurements to pair with BMI
Waist circumference is simpler and arguably more predictive of cardiovascular risk than BMI. Body fat percentage (via skinfold calipers, DEXA, or a decent bioimpedance scale) shows body composition directly. Waist-to-height ratio is a quick check — keeping your waist smaller than half your height is a solid heuristic for most adults.
Metric or imperial — does it matter?
Neither affects the result — BMI is a unitless number. Use whichever units you have your measurements in. Metric uses kg/m²; imperial uses the 703 × lb/in² shortcut, which produces an identical value when done right. This calculator converts either way, so enter whatever you know.
Frequently asked questions
What counts as a healthy BMI?▾
The WHO defines normal BMI as 18.5–24.9. Below 18.5 is underweight, 25–29.9 is overweight, and 30+ is obese (subdivided into class I, II, and III at 30, 35, and 40 respectively). These thresholds apply to adults — pediatric BMI is interpreted via age-and-sex percentiles, not these categories.
Is BMI accurate for athletes or muscular people?▾
Not really. BMI doesn't distinguish muscle from fat, so very muscular people (bodybuilders, football players, CrossFit athletes) often score as overweight or obese by BMI despite having low body fat. For these cases, body fat percentage, waist circumference, or DEXA scan are better measures.
What BMI ranges should children use?▾
This calculator uses adult categories. For children and teens (under 20), BMI is compared to age- and sex-specific percentile charts from the CDC. A BMI at the 85th–94th percentile is overweight; at the 95th+ is obese. Use the CDC's pediatric calculator for accurate results.
Does BMI account for ethnic differences?▾
The standard cut-offs were developed from mostly European populations. Asian populations tend to have higher health risks at lower BMI, so some health authorities use lower thresholds (e.g., 23 as the 'at-risk' cutoff). Pacific and Polynesian populations may have higher thresholds due to generally higher lean mass.
What if my BMI isn't in the healthy range?▾
BMI is a screening tool, not a diagnosis. A single number outside 'normal' isn't automatically a problem — talk to your doctor, who can interpret it alongside waist-to-hip ratio, blood pressure, lipid panel, and your individual history. Small sustainable changes (weekly strength training, a slight calorie adjustment) move the number more than dramatic diets.
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