... You should order one size larger!
My husband usually wears (not fitted) shirts with a collar size between 41 and 43 and we thought "are to the correct range" with a size of 42 cm in.
The "James Tyler men's business shirt, Slim Fit - Premium quality" are high-quality set of beautiful shirts, Man (n) may very well both contribute to the tie and in the free time, but through the special section, which meant more for slimmer figures is, they fall mE at least one size smaller than "normal Shirts". One should not just plan when choosing the size ...
In our case the purchased shirt was a bit cramped, but what you have sons!