In a carton of eggs, some may look slightly smaller or larger than the rest. But it isn't their size that gets them sorted into the different classes. Grouping reflects the total weight of the eggs in the carton. The classes recognized by the U.S. Department of Agriculture (USDA) are (largest to smallest): jumbo (30 ounces), extra-large (27 ounces), large (24 ounces), medium (21 ounces), small (18 ounces), peewee (15 ounces).

The USDA determines its classifications by weight of a dozen eggs per carton.

The egg shell constitutes about 13% of the weight of the egg.

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