I never really gave it much thought before raising chickens; but to sell eggs in the US, they have to be marketed according to the grade and size standards established by the USDA. The established sizes are Jumbo, Extra Large, Large, Medium, Small, and Peewee (I never knew there was a peewee size!). Sizes are classified according to minimum net weight expressed in ounces per dozen as follows:
In addition to size, all eggs sold at the retail level must be Grade B or Better, with the allowed Grades being AA, A, and B. There is no nutritional difference in the grades; it’s the appearance of the eggs that makes them one grade or another. In order to grade eggs, the exterior appearance must be judged; and the eggs must be candled to establish air cell size, albumen thickness, and yolk quality.
Sizing and grading eggs might be ok for large egg producers that have hundreds of hens; but on a small farm, eggs come in small numbers of a large variety of sizes due to the different ages and breeds of hens (they start laying peewee or small eggs as pullets, and graduate up to X-Large or Jumbo (depending on the breed) as they get older). I’m sure our hens produce AA eggs – they’re fed organically, free range on two acres, and their eggs are much fresher than those from the store – but we don’t have time to size and grade them.
Fortunately, in Ohio, you can sell eggs from the farm without sizing or grading if you identify them as “ungraded and unsized”. So, that’s how our eggs get sold – high-quality, farm fresh eggs – ungraded and of mixed sizes!