Club Shop Shirt Sizes

I live in Germany and wish to purchase some polo shirts online however not sure which size to order ie XXL, 3XL or 4XL. Looking at some old Palace Polo shirts which are XXL, flat down and I measure armpit to armpit, it is approx. 60-61 CMs. So where would that fit into the club shop size guide? Any tips, suggestions would be good.

Thanks