Hello. I know absolutely nothing about riding gear (or horses, if it comes to that) but my 12 yo niece has asked for a new riding hat for Xmas. I am unable to take her shopping to check fit as she's a 5 hour drive away, so have to buy online, which I realise is less than ideal.
I found an online guide to measuring for a hat, and sent it to my sister, who tells me DN is 54cm.
What else do I need to know?