Slate.com's "Big Money" blog is predicting a $169 million total box office take for "Watchmen" based on the opening weekend gross and the Metacritic score.
I think their total might turn out a little low. Their calculation neglects to consider several major factors: the film's running time, the film's R rating, and the month of release.
Most of the films compared on Slate's chart were June/July releases, which tend to be very front-loaded because, during the summer's movie glut, the blockbusters come in rapid succession, often with only a week to make a mark. Theater booking and marketing is designed to really front-load those releases.
The film's three-hour running time also reduces the number of showings per screen, so there were less screenings of "Watchmen" per screen than there might have been for a shorter movie. That means there are likely to be viewers turned away from sold out shows, who will come back next weekend.
The film's R rating and its source material in a 1980's era comic book may also skew the audience older. Adult viewers are relatively less likely to pack a theater on the release weekend.
On the other hand, "300," a 2006 R-rated March release from the same director, also with mediocre reviews, roughly tripled its opening weekend take, so there may be something to Slate's model.