Calculate your Body Mass Index with metric or imperial units
A BMI calculator works out your Body Mass Index — a single number derived from your height and weight that places you into a broad category from underweight through normal, overweight and obese. The formula divides weight by height squared, giving a quick, standardised figure that health bodies use as a rough screening tool across large populations. You enter your height and weight in metric or imperial units and get your BMI value along with the category it falls into.
BMI is popular because it is simple and needs only two measurements, but it is important to understand what it does and does not tell you. It is a population-level screening number, not a diagnosis or a measure of health or body composition: it cannot distinguish muscle from fat, so very muscular people can read as "overweight" while it may understate risk for others. Treat it as one quick indicator among many. This tool calculates everything in your browser, so the figures you enter stay on your device.
BMI is your weight in kilograms divided by your height in metres squared (kg/m²). The imperial version uses pounds and inches with a conversion factor. The same formula underlies both, which is why height and weight are the only inputs needed.
The common ranges are underweight below 18.5, normal 18.5–24.9, overweight 25–29.9 and obese 30 or above. These are general population thresholds, not personal targets, and the boundaries are approximate guides rather than sharp lines.
No — it is a rough screening tool, not a health assessment. It cannot tell muscle from fat or show where fat is stored, so athletes may read high while the number may miss risk in others. Use it alongside other measures and professional advice, not on its own.
Because BMI only uses height and weight and muscle is denser than fat, a very muscular person can weigh enough to land in the "overweight" range while having low body fat. This is the clearest example of why BMI is a population screen, not an individual diagnosis.
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