not too small. if they are tiny, or crushed into a powdery consistency, the hens will not be able to absorb the calcium.
this is about how small i crush mine.
yes… that huge bag of egg shells equals a half a sandwich bag.
it takes me about a week to get that much, most of the time, but it’s so worth it.
you’re supposed to offer the egg shells in separate dish next to their feeders, so the hens can eat them at will. but since my girls free range a lot, i take this little bag down to the treat dish in the afternoon, yell “treat” and wait till they gather around 