The sizes of some ships are disputed strongly within fandom, notably those of the Millenium Falcon from Star Wars and the Eagle from Space: 1999. I prefer to use the size of the full-size exterior of the Falcon, and the EagleTransporter size derived by Roberto Baldassari, at 27.25 metres and 30.9 metres respectively. The Danube class Runabout is firmly established to be 23.1 metres in length.
Even more contentious is the debate over the size of the USS Enterprise NCC-1701 in the new 2009 Star Trek movie directed by JJ Abrams. Figures released by animators at ILM stated that it is 735 metres long. This is larger than the USS Enterprise NCC-1701-E's 685 metres length, but it still appeared to be detailed at a size matching the refit from the first six movies. It later turned out that the ship had been designed with a length of only 366 metres, and rescaled to match a single ambiguous FX shot.
Luckily, Polar Lights chose a compromise scale for their model kit, due out in 2010. "Officially" 1/2500 scale, it works out to by nearly 1/1000 scale at the original design size.
The EAS Omega from Babylon 5 is about a mile long, compared to the refit Enterprise at 304 metres.
...And just how big was the IAS Excalibur from Crusade? Bloody big, that's how big it was!
But that's just peanuts compared to ... er, the Imperial Super Star Destroyer from Star Wars at a full 19 kilometres, here show in comparison to the Enterprise-D.
At the other end of the scale, we have the fighters: the Rebel X-wing at 12.3m, the Y-wing at 23.4m, the Imperial TIE-X1 at 9.2m and the standard TIE at 6.03m, versus Starfleet's Type 7 Shuttle at 8.5m, Type 6 Shuttle at 6.4m, and the Type 15 Shuttlepod at 3.6m.
And then there's theRed Dwarf, 6 miles (10 kilometres) long, also compared to the Enterprise-D.
But the Starbug is a much more manageable 21.3 metres in length, comparable to Starfleet's Danube class Runabout at 23.1 meters long.
Firefly's Serenity is 63 metres long as compared with Star Trek's Danube class Runabout at 23.1 metres long.
Stargate SG-1's Stargate is 6 metres in diametre as compared with Star Trek's Type 6 Shuttlecraft at 6.4 metres long.
Battlestar Galactica Classic's Galactica is a nautical mile (1843 metres) long, while the new Galactica is 1437 metres long, compared with Star Trek's Enterprise-D at 642 metres in length.
The Classic Viper is 8.5 metres long, the new Viper Mk.II is 8.4 metres long, the Viper Mk.VII is 9.8 metres long, the Raptor is 8.6 metres long and the Type 6 Shuttlecraft is 6.4 metres long.
Most SF series have small, light fighters or attack craft which engage in sapce combat.
Doctor Who's TARDIS, or Time and Relative Dimensions in Space Type 40 TT Capsule is about 2.5 metres tall on the outside, as compared with Starfleet's Type 15 Shuttlepod at 3.6 metres long.
Starfleet's Type 15 Shuttlepod at 3.6 metres long compares well with Volkswagen's Golf at 4.18 metres long..
The original size comparison: the USS Enterprise NCC-1701-A with the USS Enterprise CVN-65. Also shown are a Soviet Typhoon class submarine, the seaQuest and the Seaview.
Of course, no ship comparison would be complete without comparing the NSEA Protector NTE-3120 and the USS Enterprise NCC-1701, as well as their respective shuttlecraft. GalaxyQuest was, of course a parody of Star Trek - In fact, NTE stands for "Not The Enterprise".