Get on Giro's website and check the actual sizing of your helmet in centimeters or inches then compare to other helmets. I have an E2 from a couple years ago that says XXS/XS. I'm not sure if they still make the smaller helmets using this sizing system, but you really need to know the actual inches or centimeters to compare sizes in your search.

Bubba has the opposite problem and if he ever cracks his current helmet, he'll have to stop riding. I have no clue what we're going to do because Giro doesn't make the really big ones any longer.