IMDB :

"It seemed like summer at the box office over the weekend. Not only did some areas of the West experience a heat wave and temperatures in the East surge to their warmest levels of the year, but kids packed movie theaters as if mid-year recess were in full swing. The comic book-like 300 took in an estimated $70 million, a record for a March opening. Analysts had expected a huge opening -- somewhere in the neighborhood of $45 million -- but none had predicted an opening that big. The film had a reported budget of $60 million. The results were all the more surprising since the film had an R rating. (It had also received decidedly mixed reviews from critics.)"