Ballet requires grace and precision, as well as the ability to execute a step cleanly; extra weight is often seen as an impediment to this. An added consideration is that choreography often calls for a ballerina to be lifted by a male dancer. Too much excess weight can lead to injury in this situation for both the male dancer and the ballerina being lifted. A dancer who is short of stature can have an advantage in being easier to lift. In addition, shorter ballerinas are more likely to be smaller than their male partners, an advantage since ballets often portray conventional relationships, such as prince and princess, in which the man is likely to be taller.
Sometimes a ballet company isn't looking for a dancer of a particular height but rather a dancer who will be the same approximate height as the rest of the company. Ballets incorporate choreography that requires dancers to be lined up in a row, and a dancer who is 4 feet tall would not work as well aesthetically with a company comprised primarily of dancers who are over 5 foot 5 inches tall.
Male ballet dancers are taller than their female partners in general, because of the roles they portray, although a director can make an artistic choice to cast a princess that is taller the prince. Exceptions to conventional height standards are made if the dancer is gifted enough. At 5 foot 7, Mikhail Baryshnikov was considered short to dance male leads, but he remains one of the greatest ballet dancers of all time.
Although there is, in general, a greater variety of dancer's heights to be found in American companies, the Europeans stick to a more uniform standard. The minimum standard of height for a woman is 5 foot 4, while for a male dancer it's 5 foot 10.