Here's a reference chart based on the USDA sizes for eggs..... (with the exception of the last two categories named by fellow BYC ers -- specifically Nonny in Queensland Aust.)My CL haven't layed yet. Egg size is determined by weight per dozen. I think .25 oz variance is allowed for any given egg. For example Jumbo's are 30 oz per dozen (841g), therefore averaging 2.5 oz (70g) apiece. Extra large are 27 oz/dozen (764g), 2.25 (64g) oz average. Large are 24 oz/dozen(680g), 2 oz (57g) average. Medium are 21 oz/dozen (596g), 1.75 oz (50g) average. Small are 18 oz/dozen (512g), 1.5 oz (43g) average. Peewee are 15 oz/dozen (428g), 1.25 oz (36g) per dozen. I'm sure about the weight per dozen but I don't remember for sure how much variance is allowed. I know you can't put a couple Smalls in with 10 Jumbos and sell them as a Large dozen because it comes out to 28 oz.. There's a standard for how uniform the size are in each dozen.
I had a barrred rock that on two occasions laid a 4 oz egg. I went out and checked on her to make sure it didn't injure her, but she was good. I looked to see if it was a world record but not even close from some accounts I saw online.
https://www.backyardchickens.com/a/charts-and-quotes
It is based on the 1/12 of the dozen sales weight for eggs...and the huge exception size eggs don't come by the dozen. :O)