To measure waist circumference, 1) locate the upper hip bone and the top of the right iliac crest, 2) place the measuring tape in a horizontal plane around the abdomen at the iliac crest, 3) ensure that the tape is snug but does not compress the skin, 4) the tape should be parallel to floor, and 5) record the measurement at the end of a normal expiration.
Men are at increased relative risk if they have a waist circumference greater than 40 inches (102 cm); women are at an increased relative risk if they have a waist circumference greater than 35 inches (88 cm).
There are ethnic- and age-related differences in body fat distribution that may affect the predictive validity of waist circumference as a surrogate for abdominal fat.
Heterogeneity of composition of abdominal tissues, in particular adipose tissue and skeletal muscle, and their location-specific and changing relations with metabolic factors and CV risk factors in different ethnic groups do not allow a simple definition of abdominal obesity that could be applied uniformly. In particular, Asians appear to have higher morbidity at lower cutoff points for waist circumference than do white Caucasians.

National Institutes of Health, National Heart, Lung, and Blood Institute, NHLBI Obesity Education Initiative, North American Association for the Study of Obesity. The practical guide to the identification, evaluation, and treatment of overweight and obesity in adults. NIH Publication Number 00-4084. October 2000.
Misra A, Wasir JS, Vikram NK. Waist circumference criteria for the diagnosis of abdominal obesity are not applicable uniformly to all populations and ethnic groups. Nutrition. 2005;21:969-976.