Not crazy just what we know as 'italian' sizing. More specifically 'cyclist' body sizing, not normal 'general public' (overweight) sizing haha 
Lets just say I own a Ben Sherman polo shirt in XS I bought over in the states (American sizing), a UK size would be between S or M. Cycling sizing it would be an XL!
Different cycling brands size differently. It's like the high-street but much worse! The more traditional the company the closer to that italian sizing you generally find them. Castelli & Sportful very similar (Sportful slightly more relaxed). Rapha a little more relaxed again (apart from their Pro range). Endura/DHB etc is closer to your 'normal' highstreet sizing, but not quite.

Lets just say I own a Ben Sherman polo shirt in XS I bought over in the states (American sizing), a UK size would be between S or M. Cycling sizing it would be an XL!

Different cycling brands size differently. It's like the high-street but much worse! The more traditional the company the closer to that italian sizing you generally find them. Castelli & Sportful very similar (Sportful slightly more relaxed). Rapha a little more relaxed again (apart from their Pro range). Endura/DHB etc is closer to your 'normal' highstreet sizing, but not quite.
