@gnz Thanks for reaching out!
This is a good and timely question, as we are rethinking the in-store experience for items that need to be tried on. At this time we do not have try on helmets available for customers in our stores. We spoke with the Salt Lake City team and they are able and willing to help talk you through the metric conversion of your head measurement and advise fit for you if you'd like.
Hopefully this helps, thanks!