Update: This has been successfully printed and fits well (23.5" diameter head). I have also added cut files in various sizes to simplify your printing.
This is my rendition of Rick Hunter's (Hikaru Ichijo's) pilot helmet from Robotech (Macross). A classic 80's anime that I enjoyed.
It is 1 to 1 actual size and should fit an average adult. You will need to cut it to fit your particular printer.
I have not yet printed this myself, but will when I get a chance and upload images.
Good luck on your builds and I hope you enjoy this as much as I enjoyed making it.
As usual, this was built entirely in TinkerCad.