Correct way to write "R rated"

[Michelle Graciano]

Would I write "R-rated" or "R rated" as in the sense that "The movie was R rated."

[Brenda Rogers]

Ditto.

[Pat Porter]

I think, based on Morson Rule 158 (use a hyphen when a letter is used as an adjective, a prefix, or part of a verb), it would be: The movie was R-rated.

She gives an example: My car was T-boned when the van ran the light.