Waist-to-Hip Ratio vs. BMI vs. Waist Circumference Alone
BMI measures overall weight relative to height and is a quick, simple general screening tool; waist circumference alone measures absolute abdominal fat and is a strong, simple indicator specifically of abdominal health risk; waist-to-hip ratio adds a relative dimension — comparing abdominal fat against hip measurement — capturing body shape and fat distribution in a way that's independent of a person's overall body size, making it especially useful for comparing risk across people of meaningfully different heights or frames.
None of these three measures is universally "best" — each captures a genuinely different aspect of body composition and risk.
What each measure captures that the others don't
BMI's strength is its simplicity and long track record as a general population screening tool; waist circumference alone is a direct, simple proxy for abdominal fat without needing a second hip measurement; waist-to-hip ratio's specific strength is normalizing abdominal fat against an individual's own frame size (via the hip measurement), which can matter more when comparing risk between people of very different body sizes.
Why many health guidelines recommend more than one
Because each measure has blind spots the others cover, many current health guidelines suggest using waist-to-hip ratio or waist circumference alongside BMI, rather than relying on BMI in isolation, precisely to catch the abdominal-fat-related risk that BMI alone can miss.