Giro helmet sizing.

Looking at getting a Giro helmet. Have previously had Met, Specialized and Catlike (Whisper Plus), all in medium. What’s the fit like in Giro’s? Don’t really want to try one on in a shop and then buy online.

Had the older catlike compact pro in a medium, currently using giro air attack in medium. Also had another giro lid in a medium (forgot the model)

Thanks. I asked two other friends and they said the same thing. I took a punt on online ordering seeing I had a discount code.