Rock climbing shoe manufacturers size their shoes differently and each design has a unique fit. In general, a climbing shoe should have a snug fit so that there is no dead space and no hot spots. If a shoe’s upper is made out of a synthetic fabric it will not stretch. On the other hand, an un-lined leather shoe will stretch quite a bit, at least one size, after it breaks in during a day of climbing. Also, keep in mind that your feet will swell during the day and could increase a half to a full size during a day of climbing. Be sure to familiarize yourself with how different shoe manufacturers size their shoes and their recommendations for the fit of their shoe designs.