Why waist measurements matter beyond BMI
Where body fat is stored matters for health risk, not just how much of it there is. Fat stored around the abdomen (visceral fat) is more strongly linked to cardiovascular disease and type 2 diabetes risk than fat stored elsewhere on the body — which is why waist-based ratios can flag elevated risk even in someone whose BMI falls in the "normal" range.
Waist-to-height ratio — a worked example
Formula: waist circumference ÷ height, both in the same units. The widely cited rule of thumb, from research by Ashwell and colleagues, is to keep your waist under half your height (a ratio below 0.5).
A waist of 85 cm and a height of 170 cm gives a ratio of exactly 0.50 — right at the threshold, and classified as "increased risk" rather than "healthy," since the healthy band requires strictly under 0.5, not merely at or below it.
Waist-to-hip ratio — a worked example
Formula: waist circumference ÷ hip circumference. WHO's cutoffs are sex-specific: for men, under 0.90 is low risk, 0.90-0.99 is moderate, 1.0 or above is high; for women, the thresholds are lower — under 0.80 low risk, 0.80-0.84 moderate, 0.85 or above high.
A man with an 90 cm waist and 100 cm hip has a ratio of 0.90 — right at the boundary between "low risk" and "moderate risk," landing in the moderate-risk band since the low-risk band requires strictly under 0.90.
How they differ in practice
Waist-to-height ratio uses a single, sex-neutral threshold (0.5) and needs only two measurements you likely already know or can measure easily. Waist-to-hip ratio needs an additional hip measurement and uses different thresholds for men and women, reflecting that healthy hip-to-waist proportions differ by sex — but it can be more informative for tracking fat redistribution specifically (e.g. the classic "apple" vs "pear" body shape distinction; a low waist-to-hip ratio despite a high waist-to-height ratio suggests fat carried more broadly rather than concentrated at the waist).
Neither replaces the other — many clinicians consider waist-to-height ratio the simpler, more broadly applicable screen, while waist-to-hip ratio adds sex-specific nuance useful in a fuller risk assessment.
What to do if you're near a threshold
Being right at a threshold, as in both worked examples above, isn't a diagnosis — it's a signal worth paying attention to, especially in combination with other risk factors (family history, blood pressure, blood sugar). These ratios are screening tools, not medical assessments; discuss elevated results with a doctor rather than self-diagnosing from a ratio alone.