which combine with the shape categories to produce 9 categories. Proportions and dimensions The circumferences of bust, waist, and hips (BWH) and the ratios between them are a widespread method of identifying different female body shapes. As noted above, descriptive terms used include "rectangle", "spoon", "inverted triangle", and "hourglass". The waist is typically smaller than the bust and hips, unless there is a high proportion of body fat distributed around it. How much the bust or hips inflect inward, towards the waist, determines a woman's structural shape. The hourglass shape is present in only about 8% of women. A woman's dimensions are often expressed by the circumference around the three inflection points. For example, "36–29–38" in US customary units would mean a bust, waist and hips. Height will also affect the appearance of the figure. A woman who is 36–24–36 (91–61–91 cm) at height will look different from a woman who is 36–24–36 at height. If both are the same weight, the taller woman has a much lower body mass index; if they have the same BMI, the weight is distributed around a greater volume. A woman's bust measure is a combination of her rib cage and breast size. For convenience, a woman's bra measurements are often used as a proxy. Conventionally, measurement for the band of a bra is taken around the torso immediately below the breasts, with the tape measure parallel to the floor. Bra cup size is determined by measuring across the crest of the breasts and calculating the difference between that measurement and the band measurement. The waist is measured at the midpoint between the bottom of the rib cage and the top of the 'front' hip bones. The hips are measured at the largest circumference of the hips and buttocks. Fashion models The British Fashion Model Agents Association (BFMA) says that female models should be at least tall and proportionately around 34–24–34" (86–61–86 cm). Laws "aimed at preventing anorexia by stopping the promotion of inaccessible ideals of beauty" have been introduced in a number of European countries, to regulate the minimum actual or apparent BMI of fashion models. "Under World Health Organisation guidelines an adult with a BMI below 18.5 is considered underweight, 18 malnourished, and 17 severely malnourished. The average model measuring 1.75m (5ft 9in) and weighing 50kg (7st 12lb) [110lb] has a BMI of 16". Cultural perceptions According to Camille Paglia, the ideal