I had a Barred Rock and a Rhode Island Red that both laid smaller eggs. They were similar in size to medium eggs you’d find in the store, and had slight variations from egg to egg, but were pretty consistently small. My neighbor, who also has chickens, commented once on how tiny they were compared to hers, which is when I first wondered the same thing you did. I will be curious if this new batch of birds of mine have some larger size eggs or not.