US size 9 refers to a standard shoe size used in the United States. It typically corresponds to a foot length of about 10.5 inches or 26.7 centimeters. This size is commonly worn by both men and women, although the fit may vary between genders due to differences in shoe design. In women's sizing, a US size 9 usually translates to a European size 40 or a UK size 7. For men, it corresponds to a European size 42 or a UK size 8. Understanding these conversions can help when shopping for shoes internationally or online.