BMI Calculator
BMI and its limits
Body Mass Index is a simple weight-to-height ratio used to classify people into underweight, normal, overweight, and obese categories. It's a population-level screening tool — useful for tracking trends across millions of people, but unreliable for individuals with unusual body composition.
Athletes with high muscle mass often register as 'overweight' or 'obese' despite low body fat. Older adults with muscle wasting can register 'normal' while carrying unhealthy amounts of visceral fat. For individual health, waist-to-height ratio and body fat percentage are more informative than BMI alone.
Frequently asked questions
What does my BMI actually mean?
BMI (Body Mass Index) is weight in kilograms divided by height in meters squared. The standard categories: under 18.5 = underweight, 18.5–24.9 = normal, 25–29.9 = overweight, 30+ = obese. It's a population-level screening tool, not a personal health diagnosis.
Why is BMI considered inaccurate for some people?
BMI doesn't distinguish between muscle and fat. A muscular athlete can register as 'obese' BMI-wise while having low body fat. Conversely, someone with normal BMI can have high visceral fat ('skinny-fat'). BMI is least accurate at the extremes and for very tall or very short people.
What's a better measurement?
For body composition: DEXA scan (gold standard, ~$50–150), hydrostatic weighing, or bioelectrical impedance scales (cheap but inaccurate). For cardiovascular risk: waist-to-height ratio (keep under 0.5) correlates better with heart disease than BMI. For fitness: lean body mass and body fat percentage separately.
How often should I weigh myself?
Daily for trend-tracking (weight fluctuates 2–5 lbs day to day based on water, food timing, and hormones — look at weekly averages, not daily numbers). Weekly for most people. Less often if the number triggers anxiety — behaviors matter more than the scale.
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