CEO Christopher Dodd announced the tweaks in Las Vegas Tuesday at the annual movie-theater convention, CinemaCon.
The White House has called on the movie industry to give parents better tools to monitor violence in media since the Newtown, Conn., school shooting.
Dodd did not address the shooting directly but spoke generally about the need to help parents control what their kids see.
The new ratings system will include descriptions about why a movie received its ratings.
For example, the rating might cite “strong carnage” or “war violence.”