A muscular 180 cm person at 95 kg is BMI-obese and waist-healthy. A sedentary 180 cm person at 78 kg is BMI-healthy with a 95 cm waist and a ratio of 0.53.
BMI is mass over height squared, and mass has no idea what it is made of. Muscle weighs more than fat and sits in the wrong place for the formula, so athletes are routinely misclassified upwards. The more common and more dangerous error runs the other way: normal-weight central obesity, where the scales say nothing is wrong and the tape measure says otherwise. Waist-to-height catches both because it measures shape rather than amount.
Neither number is a diagnosis and disagreement does not automatically favour the waist. BMI remains the better predictor at a population level and is what most published risk tables are built on, so a clinician using it is not being lazy. Waist measurement is also the less reproducible of the two — landmark placement, tape tension and whether you breathed out move it by centimetres, which is more than the difference between two adjacent risk bands.
Estimate with the rule, then check it against the calculator that models it properly.
Open Waist-to-Height Ratio →A muscular 180 cm person at 95 kg is BMI-obese and waist-healthy. A sedentary 180 cm person at 78 kg is BMI-healthy with a 95 cm waist and a ratio of 0.53. BMI is mass over height squared, and mass has no idea what it is made of.