American or NATO size to European Size Conversion?

Ok so I'm trying to buy these Russian blue tiger camo pants online because I like the way it looks but the site is asking me for my size and its in the European format that I am not familiar with. My pants size are 40 x 32. For a pair of BDU's I have, I am X-Large Long. My NATO size is 8390/9909. I am 5'9 (if that helps). I am getting options like 48/182, 48/188, 58-60/176, just to name some. Any help with this issue will be greatly appreciated.