What Size Wool Slider do I need?

What size Wool Slider do I need?

7" Mini Tray ---> Small Wool Slider

8" Mini Tray or 8" Deep Dish Tray ---> Medium Wool Slider

9" Classic Tray ---> Medium Wool Slider

11" Mini Tray, 11" Deep Dish Tray or 12" Classic Tray ---> Medium Wool Slider

12" Classic Tray ---> Medium Wool Slider

15" Classic Tray or 15" Deep Dish Tray ---> Large Wool Slider

18" Classic Tray or 18" Deep Dish Tray ---> Large Wool Slider

20" Deep Dish Tray ---> Large Wool Slider