Ok, so here's the story.  I have a large Maine coon mix cat, so I bought this XL costume.  It was made for a dog, so the legs were long.  I cut the sleeves up and the bottom too.  I will add photos later.  It was stored in the attic, so a few of the Jason masks sticky appliques became stuck together.  However, the mask is in tact and really is more appropriate for a dog (it's just larger than a car face no matter how big the cat- ideal for average cat is probably L).  The jersey is still good wearable and I kept the bottom piece.  I will add photos tonight, but if you're interested just send me an email- I'd be happy to chat.  This costume made for some great pics.

Size Chest* Neck* Breed Examples
Extra Small 12 7 Teacup and Puppies under 5 lbs
Small 14 11 Chihuahua, Pomeranian, Australian Terrier, Yorkshire Terrier, Toy Poodle
Medium 17 25 Pug, Maltese, Jack Russeli Terrier, French Bulldog, Boston Terrier
Large 20 22 Bichon Frise, Beagle, Cocker Spaniel, Corgi, Scottish Terrier
Extra Large 24 28 Springer Spaniel, Brittany Spaniel, Collie, Bulldog, Schnauzer