Box office figures are sometimes adjusted, but within the industry it is sort of an academic exercise, (we live now and it’s real money that counts). Further, all this stuff about ‘highest weekend box office’ and ‘most successful film ever’ is of course very marketing oriented and marketing execs tend to read the stats like the devil reads the Bible. As Twain said; ‘Lies, goddamn lies and statistics’.
In any case, adjusting to inflation doesn’t really do the trick since ticket prices have tended to go up slightly above inflation, so what is done instead is to take the number of admissions and multiply with a current ticket price.
In flat dollar amount the top grossing film at the cinema (video sales and rentals, pay per view and TV distribution not accounted for) is Titanic with a whopping 1.8 billion dollars, followed by Harry Potter at somewhere above 950 million and Star Wars Episode I at approx. 920 million.
Since I’m not in the office right now and I don’t have access to any really good databases from here, I can’t give you the exact figures for adjusted worldwide performance. However, boxofficemojo.com gives us the adjusted figures for the US were number one is Gone With The Wind followed by Star Wars – A New Hope and third is Sound of Music. Titanic is number seven while Harry Potter and Phantom Menace don’t even make it into the top ten. IIRC it’s the same films when counted worldwide, but I can’t swear on it.
Last but not least opening weekend grosses are only sensible to compare back into the 80s. Before that the philosophy of distribution and marketing was very different in as much as that a film would be given time to grow an audience, while nowadays a release is most often preceded by a heavy marketing effort leading to a smashing opening with a relatively short theatrical life, with pay per view, video and DVD releases following quite soon after. The next step, were LOTR and Episode II are forerunners will be simultaneous worldwide releases. In any case with 114 million, Spider Man has reached the uncontested all time number one opening weekend box office in the US, even after inflation adjustment.
For more box office info:
The Internet Movie Database
Box Office Mojo