from the Box Office Mojo article:
It was a dollar-spangled debut for Captain America: The First Avenger. Despite being the last to strike, the most famous superhero of Summer 2011's comic-book onslaught delivered the best opening salvo of the bunch, while Harry Potter's last stand fell prey to the adage, "the bigger they are, the harder they fall."
Captain America made an estimated $65.8 million on approximately 7,100 screens at 3,715 locations, edging out fellow Avenger Thor's $65.7 million as well as Green Lantern's $53.2 million and X-Men: First Class's $55.1 million to top the summer's superhero launches. While the gross difference was a sliver, Captain had nine percent greater estimated attendance than Thor, which received more bolstering from 3D (and had IMAX): Captain's 3D share was 40 percent at 2,511 3D locations, compared to Thor's 60 percent at 2,737.
In terms of estimated attendance, Captain America's first weekend was slightly ahead of G.I. Joe: The Rise of Cobra and Watchmen but, among past July Marvel Comics kick-offs, it trailed Fantastic Four and X-Men by sizable margins. Distributor Paramount Pictures' exit polling indicated that 64 percent of Captain's crowd was male (about the same as Thor) and 58 percent was 25 years of age and older (skewing younger than Thor's 72 percent).