7"-6 1/2" is a good enough estimate. I just didn't want to end up with a yarmulke or a facemask with no eyes.
Good thing I double checked the standards chart, I was on preemies for the 12". Baby is 14", toddler is 16".
The 12" band stretched to my 24" head so I'm going to go with 14".
I did email my niece to send me some measurements but I imagine that has been met with extreme confusion, both as to why I'm asking, how to measure and what to measure with. The craftiness that has been in my family for generations skipped her generation.