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body mass index
Body mass index divides weight in kilograms by height in metres squared — a screening measure that correlates with body fat across populations and drives the WHO categories shown. Its virtue is simplicity: two measurements anyone can take, comparable worldwide. The healthy-range row inverts the formula to show the weight span corresponding to a normal BMI at your height.
BMI can't see composition: muscular athletes read overweight, and normal-BMI bodies can carry high visceral fat ('skinny fat'). It also shifts meaning at the extremes of height and in older adults, and thresholds arguably sit lower for some Asian populations. Treat it as a first filter — the waist-to-hip, body fat and combined health-risk calculators on this site each add the dimension BMI lacks.