How do i know what my size of the shirt?

So I was planning to get Deluxe edition of the game (Early Bird + Coaster Head)
But the problem is the shirt size. I'm not sure what size that I can wear.

Is there any measurement for the shirt? Thank you in advance!

Sorry for my bad english. ;-;
Yes, even though there aren't any exact measurements there are some guidlines for the size S, M, L XL and XXL. Search for "shirt size" on google/google images and you'll find plenty of results.