GlobalSecurity‘s striking comparison of Aircraft Carriers by country.
From GlobalSecurity.org: (my emphasis)
An aircraft carrier is a ship that is capable of operating fixed wing aircraft, including jump-jets such as the Harrier. America has nearly twice as many aircraft carriers – 20 – as the rest of humanity combined – 12 – and America’s aircraft carriers are substantially larger than almost all the other’s aircraft carriers. The Navy likes to call the big Nimitz class carriers “4.5 acres of sovereign and mobile American territory” — and all twenty American carriers of all classes add up to nearly 70 acres of deck space. Deckspace is probably a good measure of combat power. The rest of the world’s carriers have about 25 acres of deck space, approximately one third that of America’s [until 2011, this number was only 15 acres, but new Chinese and Italian vessels upped the total appreciably].