They are generally smaller than eggs from standard hens, but it also depends on the breed. Some bantam breeds lay slightly larger eggs than other bantam breeds.
I have standard and Bantam chickens, and the bantam's shells are smaller and they don't need as much space, but their yolks are just a big as the standard chickens!!!! You can't tell them apart!!!
This is my first year with bantams. They are silver penciled rocks & have been laying since October. They vary right now between 1 ounce & 1 1/4 ounces. I still do not see the "big yolk" or more yoke than white compared to a large egg that everyone talks about. My ratio of yolk to white seems the same as a regular egg. We love using the little eggs!
Thanks, everyone, for your responses! And thank you for posting that pic, Greencastle, that is really neat to see! I am surprised at how big some of the bantam eggs can be!