Consumers often spend a few puzzled moments looking at egg cartons in supermarkets. That's because there are six official egg sizes. The sizes are determined by weight. A jumbo,the largest-size egg, weighs 30 ounces while a peewee egg, the smallest size, weight only 15 ounces. In between are extra-large, large, medium, and small eggs. Most markets only stock the four largest sizes; small and peewee egg are usually sold to bakers and companies in the food processing business.