The three theatrical cuts of The Lord of the Rings film trilogy have a combined running time of 558 minutes. That total comes from 178 minutes for The Fellowship of the Ring, 179 minutes for The Two Towers, and 201 minutes for The Return of the King.
The figure applies to the original theatrical editions, not the longer extended editions released for home viewing. Each extended edition adds substantial material, so totals quoted for the complete trilogy can differ depending on the version.
The increasing length of the final film reflects its many simultaneous storylines, including the battles in Gondor and the journeys of Frodo, Sam, and Gollum. Despite the scale, the theatrical trilogy was released as three annual films.