What is the perfect length of time for a movie? Is it an hour and a half? Two Hours? Three hours? What is the right amount of time to tell a story? Well, that depends on the story. The film's genre directly affects the attention span of the audience. While the values below won't cover every film in a given genre -- as every story really is different -- it will, we hope, do a solid job of explaining the target length of an example typical of its type.
Horror: 90 minutes
Amongst the shortest films out there, today's horror movies are rarely like the slow, developing, almost lumbering tales of old. We've thrown most character development out the window in this genre and are left mostly with the money shots of gore, nudity, and a good, old-fashioned jump scare or two. And that rarely holds an audience's attention for more than 85 minutes. If you hit 90 minutes in a horror movie, it better be a unique idea or chock full of interesting characters -- otherwise, your audience is bound to tune out.
Romantic Comedy: 100 minutes
Half brother and estranged sibling of the horror movie, the Romantic Comedy relies entirely upon formula to tell its story. A new, original idea in a rom-com means that you've found an untold way for our lovers to meet and fall in love. No matter what ideas you come up with, the film must revolve around boy meets girl, boy loses girl, boy gets girl back. If it doesn't, it's not really a romantic comedy. Rom-coms are gifted with an extra 10 minutes or so to do their thing as they revolve almost entirely around conversation and character development, and pad out time between emotional beats with the occasional montage usually set to a well-known pop song. If you find one approaching the two-hour mark, it better sport a bevy of characters or be wrestling with complicated issues -- otherwise you'll find the audience drifting and wondering when these idiots will just admit they love each other already.
Thrillers: 120 minutes
A thriller is a horror movie without all the gore and supplemented with broader (supposedly) real-world problems and mysteries in place of the monster. While they often follow almost the exact same structure as a horror movie, they usually have slightly better developed characters and very complicated ideas to express and explain to the audience. This is what typically fills in the additional half hour. Any shorter than this and you are skimping on the characters, the action, or -- worst of all -- the original ideas. Any longer and the film should be labyrinthine and quite possibly based upon a true story.
Epic Science Fiction/Fantasy: 150 minutes
Good fantasy and science fiction takes the structure of another type of film and sets it in another world entirely. The extra time in these films rarely involves deeper character development or story progression and instead goes toward exploring this alternate reality and explaining the rules of it to the audience (as well as to a character in the film). Occasionally, adapted works tend to contain far denser narratives than works scripted originally for the screen, but that's not always the case. Much shorter than 150 minutes and your audience will feel cheated; much longer and your name better be Jackson or Cameron.
Michael Bay-style Action Films: 150 minutes
Michael Bay makes action films differently than everyone else in the world. He doesn't seem to like three-act structure very much. Instead, his films almost play with a Shakespearean five-act structure. Just when you think a Bay film is over -- around the 90-minute mark -- an unseen plot twist ramps up the fourth act and takes the film in a wildly new direction. Bay uses all this additional time not to tell a story, but rather to demolish additional locations, often in another country entirely.
Luc Besson-style Action Films: 90 minutes
The antithesis of the Bay style of film, Besson-style films tend to be very wham, bam, thank you ma'am. The film introduces us to a character -- who is usually a world-class driver/assassin/spy/cop (or, occasionally, all of the above) -- and then has someone piss him off. Then he either runs from them or chases them until about the 90-minute mark. These films rarely have a single moment of wasted screen time. If your film has a second main character -- like the Fast and the Furious films -- add an extra 15 minutes to develop them; otherwise, going over 90 minutes means you slowed down too much or have exhausted the audience.
Indiewood Pictures: 120 minutes
Indiewood films are those supposedly independent films with respectably small budgets and a star-studded cast. Think Little Miss Sunshine. There's often very little independent about them, but they do tend to thumb their nose at convention and feel different from the usual studio gobbledygook many of these A-listers are typically offered. A good Indiewood film never goes over two hours; any more than that and they are usually bogged down in pretension.