I ordered this to wear under an I Dream of Jeannie Costume to be more modest and it really works well for that purpose for me. I must say that I don't believe it would really fit someone who is a size 12. The pants are like a standard medium and are about two inches above my ankles. I would say the top is a standard small. I'm planning on cutting the elastic out of the neckline because it's rounded and not the more v-neck it shows in the picture. I am really pleased with it though. It's just what I needed. Thirteen dollars for something to wear underneath a costume that's comfy and not see-through. The headband would probably be too tight for an adult too. I am 5'5" 115 lbs.

I have some pictures I plan on posting of the top. (Forgive my grungy basement, please.)

Hope this helps~