"All of the KH satellites, of which more than 150 have been launched, consist of film cameras or electro-optical cameras that view the ground through telescopes. KH-7 and KH-9, the Gambit series, had resolutions of about 7 and 2.5 centimeters respectively. The KH-9 Hexagon satellites had 5 to 10 meter resolutions. It is not clear from any of the Internet sources consulted when 1) parachute drops ceased and 2) when electro-optical scanners replaced film. But, KH-11 is designated as an ELINT type (Electronic Intelligence) and did relay its imagery to receiving stations. The KH-11 Crystal satellites produce both SWIR and Thermal Infrared imagery, suggesting a non-photographic component. The KH-12 series, the last for which some specifications can be found, is reputed to achieve a resolution of 2+ cm, although images of this sharpness haven´t been released."
source:
http://rst.gsfc.nasa.gov/Intro/Part2_26e.html
donc c´est moins de 2,5 cm et c´est sans doute encore moins.