what size is the drain plug for 04 Chevrolet cavalier?

its 12x1.75 thread but the head size can vary hope this helps

go to the parts store and they will look it up and give you what you need or better yet if you can get a ride to the parts store take the old one with you, if it's leaking you might need a self tapping drain plug.

if you mean what wrench size.. its either a 13mm or a 15mm. good luck.

its probably a 13mm.