Measure your foot heel-to-toe, look over the size chart for the particular shoe you're considering. Unfortunately not all brands tell you the width, or foot volume.
My feet measure 11.25", I usually wear US size 10.5 or 11 in most shoes, which is generally 46 or 46.5 in euro sizing. My Fizik R1 Infinitos are size 46 which fit me well using Specialized BG Red insoles. (I have flattish feet.) I would characterize the shoes as medium width, medium volume. I have a low volume instep so pick up extra space with a 1.5mm footbed in each shoe. I think they're true to size meaning if you measure your foot and look at their size charts it'll probably fit.
Edit: the insole shims I use (actually 1/16", but close enough to 1.5mm):
https://bootfittingsupply.com/#!/Ins...air/p/18247140