TDKR clocks in at two hours and forty-five minutes. In other words, it's a long film. Both of its predecessors clocked in at over two hours, but this one nearly clocks in at three.
Of course, the film has multiple objectives that prolong its running time. The film seeks to wrap up the trilogy in a satisfying fashion and introduce several new characters that play vital roles in the story. Aside from the villain Bane (Tom Hardy), the film introduces us to several major characters like Selina Kyle (Anne Hathaway) and John Blake (Joseph Gordon-Levitt).
With all of that in mind, viewers should be aware that when they take their seats, they will likely be sitting in the theater for over three hours, so people should take their bathroom break before it begins (no pun)...