Size of Executor was estimated in various works to be anywhere from 8 000 to 19 000 meters. Current official figure is 19 000 meters; however, I am not interested in "official" figures, I am interested in canon evidence. Thus, I made this page.
NOTE: Some pictures are rescaled due to excessivly large size. In that case, measurement figures are for original size.
(Transport scaling based on Falcon flyby estimate (before Rebel fleet jumps to hyperspace) is 85.5 to 95 meters (9 to 10 times the length of X-wing). I took middle value here).
CONCLUSION: Executor is 12 km long.