Calculatrice Ratio Taille-Hanche

Waist-to-hip ratio measures where body fat is stored rather than how much there is, which is the information BMI cannot provide. Fat carried around the abdomen is metabolically active and sits alongside the internal organs; fat carried on the hips and thighs is not associated with the same cardiometabolic risk. Two people with identical BMI can have substantially different risk profiles, and this ratio is one of the simplest ways to see that difference.

La formule

Waist-to-hip ratio = waist circumference / hip circumference

• Waist = measured at the midpoint between the lowest rib and the top of the hip bone, at the end of a normal exhale
• Hip = measured at the widest point of the buttocks
• Both measurements must use the same units; the ratio itself is unitless

Measurement protocol and cut-offs follow the WHO expert consultation on waist circumference and waist-hip ratio, Geneva 2008, published 2011.

How to measure correctly

The measurement is more error-prone than it looks, and most of the error is in the waist. The WHO protocol specifies the midpoint between the lowest palpable rib and the top of the iliac crest, not the narrowest point and not the navel, which sit at different heights in different people. Measure directly against skin or over thin clothing, with the tape snug but not compressing, at the end of a normal breath out.

Because a small measurement error produces a meaningful change in the ratio, taking each measurement twice and averaging is worthwhile, and repeating in the same way each time matters more than absolute precision if you are tracking change.

• Do not hold your breath or pull your stomach in; both change the result.
• Measure at the same time of day, ideally in the morning before eating, when tracking over time.

How to read your result

The WHO thresholds below define substantially increased risk of metabolic complications. They are population-level cut-offs, and like BMI they were derived largely from European-ancestry data, with lower waist circumference thresholds recommended for South Asian, Chinese and Japanese populations.

• Waist circumference alone predicts cardiometabolic risk about as well as the ratio in most studies, and it is simpler to measure reliably, which is why many guidelines now lead with it.
• The ratio is more useful than waist alone in people at the extremes of frame size, where a given waist means something different.

Why abdominal fat is different

Visceral fat, packed around the organs inside the abdominal cavity, drains directly into the portal circulation and delivers free fatty acids and inflammatory signalling molecules straight to the liver. That is the mechanistic basis for its association with insulin resistance, dyslipidaemia and hypertension. Subcutaneous fat on the hips and thighs drains into the general circulation and is not associated with the same effects.

The ratio cannot distinguish visceral fat from subcutaneous fat over the abdomen, which is a real limitation, but a high ratio raises the probability that a substantial share is visceral. Imaging is the only way to separate the two directly, and it is rarely justified outside research.

Limites

• The ratio can stay unchanged while both measurements grow, which is a real weakness: someone gaining weight proportionally shows no change in the number despite rising risk.
• Measurement technique dominates the error. Using the navel rather than the WHO midpoint, or measuring over bulky clothing, shifts the result enough to cross a threshold.
• Cut-offs were derived mainly from European-ancestry populations. Lower waist thresholds are recommended for South Asian, Chinese and Japanese populations.
• The ratio is not valid in pregnancy, and is unreliable in people with abdominal distension from ascites, large hernias or significant bloating.
• It cannot distinguish visceral from subcutaneous abdominal fat, which is the distinction that actually carries the metabolic risk.
• This is a screening measure. It does not diagnose anything and should be interpreted alongside blood pressure, glucose, lipids and clinical assessment.

Questions fréquentes

What is a healthy waist-to-hip ratio?

Below 0.90 for men and below 0.85 for women, using WHO thresholds. At or above those values, the risk of metabolic complications is substantially increased at a population level.

Where exactly do I measure my waist?

At the midpoint between the lowest palpable rib and the top of the hip bone, at the end of a normal breath out. Not at the navel and not at the narrowest point, both of which sit at different heights in different people and give inconsistent results.

Is waist-to-hip ratio better than BMI?

It answers a different question. BMI describes how much weight there is relative to height; the ratio describes where the fat is stored. For cardiometabolic risk, fat distribution adds information BMI cannot provide, which is why guidelines increasingly use both.

Why does abdominal fat matter more than fat elsewhere?

Visceral fat inside the abdominal cavity drains directly to the liver and releases free fatty acids and inflammatory mediators into that circulation, which is linked to insulin resistance and dyslipidaemia. Fat on the hips and thighs drains into the general circulation and does not carry the same associations.

Should I use waist circumference instead?

For most people it works about as well and is easier to measure consistently, which is why several guidelines now lead with it. The ratio adds most for people at the extremes of frame size, where the same waist measurement means something different.

Références

1. World Health Organization. Waist circumference and waist-hip ratio: report of a WHO expert consultation, Geneva, 2008.
2. MedlinePlus. Health risks of obesity.
3. US Department of Health and Human Services. Physical Activity Guidelines for Americans, 2nd edition.
4. MedlinePlus. Obesity.