In the Belmont Stakes, the number of horses, known as the field size, can vary substantially. In the five races run from 2010 to 2014, the average field was 12 horses.
The smallest field that has ever run in the Belmont Stakes was two horses, which happened on five different occasions. On the other hand, the most horses ever to start was 15, which occurred in 1983. On several other occasions, as many as 14 horses have run in the Stakes, including as recently as 2013. As the last race in the Triple Crown series, the size of the Belmont Stakes' field is often very important in determining whether a horse wins the third and final race, since a smaller year increases a participant's chances to win. In years where the winner also won the Triple Crown, the average field was 5.4, including the winning horse.