This was worn once to a halloween party at a school. There is no letter size but I can tell you that from the neck, measured down to the foot openings is 4 feet exactly. Each arm is 2 ft long. It was sold as a Medium. The girl that wore it was just over 5 feet tall for reference.
That said, I will take returns, but you pay return shipping so make sure you've measured the body that will wear this. :-)