Your starship is big, very big. Now how do you make this across to people? By stating how big it is in miles or kilometers. It may be a Starship Luxurious or so packed full of people or machinery that the interior resembles that of a submarine. Generally these ships are too massive to land: they're built in space and stay in space.
Often mile-long starships are considered to be "harder" than small ones, partially because a slower-than-light ship would need to be massive to carry all the fuel and supplies needed for a decades-long voyage.
Supertrope to Planet Starship and Unnecessarily Large Vessel. See also: Cool Starship, Big Dumb Object, The Battlestar and Generation Ship.
Anime and Manga
In Super Dimension Fortress Macross the eponymous Macross is an city-sized alien spaceship which crash lands on Earth, which is then used by humans to go into space. 1210 meters (3970 feet) long.
Star Wars: The infamous Imperial-class Star Destroyers are 1,600 meters long, or approximately one mile. While Darth Vader's Super Star Destroyer was 19 kilometers. However the Venator-classes shown in Revenge of the Sith were only 1,137 meters and apparently capable of landing.
Then there's the Death Star, which is the size of a small moon.
In Independence Day, the mothership has been estimated to be several hundred kilometers across, the "city-killer" Flying Saucers that detach from it are about 15 miles in diameter.
The opening scene of Saturn 3 features an enormous spaceship, meant to visit outposts on various moons and planets in the solar system at sub-light speeds.
From Iain M. Banks's The Culture novels, the General Systems Vehicles. You know that bit at the beginning of Star Wars, where the Star Destroyer swallows up the Tantive IV into its docking bay? Picture a ship that could do that... to the Death Star. Twice.
In Stephen Baxter'sXeelee Sequence universe: the Xeelee Nightfighter. The cockpit is small, about the size of a room, but its wings stretch out for kilometers in either direction, like vast sails. The purpose of these wings are never made evident, as the ship itself travels via teleportation.
E. E. “Doc” Smith's book Skylark Of Valeron: the eponymous vessel was a sphere over 1000km in radius and has a crew of four, it needed to be that big to contain the navigational instruments necessary to cross intergalactic space.
The Star Wars Expanded Universe adds enough of these that it seems kilometer-plus is fairly standard for heavy capital ships in the Galaxy Far, Far Away, particularly in the Imperial and post-Imperial eras. These are just some of the biggest examples.
"Super star destroyer" is basically a catchall term for ships following the star destroyer design philosophy and larger than about three kilometers. The Empire built many of these, but most were one-offs and only the Executor-class went into (relatively) wide production with around a dozen known.
The Eclipse-class star dreadnaught from Dark Empire is 17 kilometers long, outmasses the Executor-class, and mounts a superlaser capable of cracking a planet's crust. This won't destroy the planet, but the seismic effects will depopulate it quite handily.
By the New Jedi Order series the New Republic saw the need to have a counter for super star destroyers and the like, and the Mon Calamari supplied the 17 km Viscount-class battleship. For their part the Yuuzhan Vong had their koros-stronha or "worldships", 10 km in diameter and primarily colony ships but quite capable of defending themselves against GFFA capital ships. They also had a couple different types of kor chokk[[note]]"grand cruiser"[[/note]] of similar size that served much the same command-and-control/heavy battleship role as super star destroyers.
By the Legacy comics ships of SSD scale are seen as Awesome, but Impractical (without a galaxy-sized tax base they cost too much to operate) and no longer in use. The Fel Empire's warship of choice is the Pellaeon-class star destroyer, which is about the same length as an Imperial-class but more massive.
The two miles long Imperial battlecruiser from Foundation.
In John Ringo's Troy Rising series, Troy, Thermoplae, and Malta are 9-13km wide mobile battle stations, each using rapid fire 50 megaton nukes to power their Orion Drives and carrying an entire fleet of cruisers, fighters, and millions of missiles. They make the Rangora (the enemy aliens) Assault Vectors (which are pretty impressive battleships in their own right) look puny.
In Chindi, the alien ship they refer to as the chindi is over 16km long, and apparently uninhabited, but still intent on its unknown mission.
Ships in the Honor Harrington series are usually denoted by their tonnage rather than their length, but one book had a diagram that showed their main warships as being 2 kilometers in length for a battleship to 3km for a Superdreadnought. Then David Weber apparently realized that at that scale they were far too light and he re-scaled them so they top out at just over 1500m for an SD and 1200m for a battleship.
The Red Dwarf is 6 miles long, 5 miles tall, and 4 miles wide.
Star Trek doesn't normally go in for this, but there are a few examples.
The Deep Space Nine episode "Valiant" provides a Jem'Hadar battleship described as twice as the size of a Galaxy-class starship. A quick calculation based on the DS9 Technical Manual results in a ship just under 1.3 kilometers long. Another Jem'Hadar capital ship that is similar but much larger is seen during the Battle of Cardassia in "What You Leave Behind".
One episode of Star Trek: Enterprise has Captain Archer being taken through time and brought on board the USS Enterprise-J. Due to time constraints with making the episode, the designer of the ship admits that they only had a couple of weeks to flesh out a concept, which is only very briefly shown in a fuzzy holographic computer display in the episode itself. The ship was never shown from the outside in the episode, so supplementary material filled in for that. The Enterprise-J was built as a generational ship, capable of folding space to instantly travel to other galaxies. It is so large that it's turbolifts are replaced with site to site transporters, and it features massive parks and even an entire university on board. It's saucer is roughly 26 miles in diameter.
In the Babylon 5 spinoff Crusade, the Excalibur was 3000 meters in length, and had an internal rail line (similar to that on the Babylon 5 space station) running along its length for transportation within the ship.
Also, the Babylon 4 station, which preceded Babylon 5, had a propulsion system (unlike its successor), so could serve as a mobile base-ship and carrier that was 6 miles in length (a bit larger than Babylon 5).
The Ori warships in Stargate SG-1 were established by ancillary materials as 1.1 kilometers long.
Wraith hive ships in Stargate Atlantis were described as roughly thirteen times larger than an SGC Daedalus-class battlecruiser. This gives a ship around 2.9 kilometers long. The super-hive that appears on the series finale is even larger. Whereas Ancient city-ships such as Atlantis are 3 kilometers in diameter.
The titular Lexx is an insect-like ship that is 10 kilometers in length.
Warhammer 40,000 loves this trope. In the Imperial navy alone escort frigates and destroyers are 750 meters to 2 kilometers long, while battleships are up to 8 km.
In Mass Effect, Reaper capital ships like Sovereign and Harbinger are around two kilometers long and so massive that their kinetic barriers are severely weakened while they're landed in Earthlike gravity (due to the mass effect field strength needed to reduce their mass to the point where they don't crumple under their own weight). Citadel dreadnoughts vary by race, but average one kilometer.
The X-Universe series doesn't explicitly give lengths for its ships. However in 2009 a forum member in this thread scaled their in-game models and determined that the largest destroyers average three kilometers, with the Valhalla being the outlier at five.
Aurora Carriers are 1.2 km long, compared to the Federation and Rebel Carriers which are only 500 m long.
Polaris Ravens are 1.2 km long and about 1 km wide making them the biggest playable ship in the game.
Deimos-Class Colony Ships are approximately 3*3*3 km as the hypergates they traveled through had to be reconfigured to form wormholes with a diameter of 5km.
Titan class ships in EVE Online can be as long as 18 kilometers.
The Ultimate Starship Size Comparison Chart lines up notable ships and space stations from several different science fiction franchises (along with a few real-life ships for the sake of argument) side-by-side to compare their length. They're all dwarfed by the aforementioned Executor-class star dreadnaught from Star Wars.
Five hats means that five tropers think it is ready to publish.
You are saying that you think this draft is ready to be published. That means the description is not ambiguous,
it doesn't duplicate an existing trope, there are at least three examples, and the title makes sense.
Is that what you meant to do?
You are saying this draft has a ready-to-publish hat it does not deserve and you are taking it back.