The waist–hip ratio or waist-to-hip ratio (WHR) is the dimensionless ratio of the circumference of the waist to that of the hips. This is calculated as waist measurement divided by hip measurement (). For example, a person with a 75 cm waist and 95 cm hips (or a 30-inch waist and 38-inch hips) has WHR of about 0.79.
The WHR has been used as an indicator or measure of health, fertility, and the risk of developing serious health conditions. WHR correlates with perceptions of physical attractiveness.
Measurement
WHO protocol
According to the World Health Organization's data gathering protocol, the waist circumference should be measured at the midpoint between the lower margin of the last palpable ribs and the top of the iliac crest, using a stretch-resistant tape that provides constant tension. Hip circumference should be measured around the widest portion of the buttocks, with the tape parallel to the floor. Other organizations use slightly different standards. The United States National Institutes of Health and the National Health and Nutrition Examination Survey used results obtained by measuring at the top of the iliac crest. Waist measurements are usually obtained by laypersons by measurings around the waist at the navel, but research has shown that these measurements may underestimate the true waist circumference.
For both measurements, the individual should stand with feet close together, arms at the side and body weight evenly distributed, and should wear little clothing. The subject should be relaxed, and the measurements should be taken at the end of a normal respiration. Each measurement should be repeated twice; if the measurements are within 1 cm of one another, the average should be calculated. If the difference between the two measurements exceeds 1 cm, the two measurements should be repeated.
Practical measurement
Practically, however, the waist is more conveniently measured simply at the smallest circumference of the natural waist, usually just above the belly button, and the hip circumference may likewise be measured at its widest part of the buttocks or hip. Also, in case the waist is convex rather than concave, such as with different body types, and obesity, the waist may be measured at a horizontal level 3 cm above the navel.
Indicator of health
Serious health conditions
The WHR has been used as an indicator or measure of health, and as a risk factor for developing serious health conditions.
WHR is used as a measurement of obesity, which in turn is a possible indicator of other more serious health conditions. The WHO states that abdominal obesity is defined as a waist–hip ratio above 0.90 for males and above 0.85 for females, or a body mass index (BMI) above 30.0. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) states that "total cholesterol levels are usually higher in persons with predominant abdominal obesity, defined as a waist-to-hip circumference ratio of ≥ 0.8 for women and ≥ 1.0 for men.
WHR has been found to be a more efficient predictor of mortality in older people (>75 years of age) than waist circumference or BMI. If obesity is redefined using WHR instead of BMI, the proportion of people categorized as at risk of heart attack worldwide increases threefold. WHR may be less accurate in individuals with a BMI of 35 or higher, and more complex to interpret since an increased WHR may result from increased abdominal fat or decreased lean muscle mass around the hips. The body fat percentage is considered to be an even more accurate measure of relative weight. Of these three measurements, only the waist–hip ratio takes account of the differences in body structure. Hence, it is possible for two people of the same sex to have different body mass indices but the same waist–hip ratio, or to have the same body mass index but different waist–hip ratios.
WHR has been shown to be a better predictor of cardiovascular disease than simple waist circumference and body-mass index. The study by American Heart Association has shown that measuring waistline and comparing it to hip size might be a better way to predict heart disease risk than a widely used body mass index. However, other studies have found waist circumference (particularly Waist-to-height ratio) to be a better indicator of cardiovascular risk factors than the waist–hip ratio, body fat distribution, and hypertension in type 2 diabetes.