problem for sizes

the problem is that the size you write is just a letter but not size number that is you take the letter (L) that this size is L (42/44/46 or 48/50) so for me my pants size is 48 or 46 if the waist is elastic pants or 80% cotton 18% polyester and 2% spandex or XL or XXL correspondes therefore what these letters because no explanation as I know ais you said above thank you