Depends on the species.. someone posted a size scale of all the species once, I will try to find the link. The smallest species is like 12-14" + tail..
Dude, check out bro tyson's gallery. he has an awesome collection of huge monster rays.
i went to his house about a 3 weeks ago to visit, and is still fantasing, wet dreaming about them till today.
his largest is a tiger ray, about 26inches across in diameters i think.. super huge!
a teacup is not a type of ray what they call a "teacup" is actully a hystrix or a reticulus a tea cup is what they call any ray with the disk size of 4" or smaller