The entire series of The Legend of Korra contains 52 episodes. They are divided into four seasons, called “Books” in the series: Air, Spirits, Change, and Balance.
The season lengths are not identical. Book One: Air has 12 episodes, Book Two: Spirits has 14, Book Three: Change has 13, and Book Four: Balance has 13. Together, those seasons total 52 episodes. The episodes are also sometimes called “chapters,” reflecting the show's book-like structure.
The series was originally planned as a 12-episode miniseries. Nickelodeon later expanded it first to 26 episodes and then to 52, allowing the creators to develop four separate seasonal stories. The first episode premiered in April 2012, and the series finale aired in December 2014.
The number can be confused with 60 or 56 because the show has four seasons and a substantial mythology, but neither figure matches the official episode count. The 52-episode total refers to the animated television series itself, not later comic-book continuations.