Based on sizes given, in my opinion it sounds like medium would be the better bet!

I just got this chandelier in medium too!
The general rule of thumb is 1/2 the width of your dining table, I've also heard take the measurements of the room lengthwise and width and add them together and change to inches. So your room is 13+10= 26 (so for both methods, the Medium seems to work best) Good luck!

Right on.