The fleet charts provide a size comparison of canon Federation and alien ships. The charts only include vessels whose structure or on-screen evidence allows at least a coarse size estimation and only if a clear side view is available. Please note that not necessarily the "official" sizes as in print publication are listed. Many ship sizes are controversial because even the screen evidence may be contradictory.
Fleet Charts in TIFF Format - the above charts in the same resolution but higher quality
Fleet Chart Annotations - the above charts, along with the sources and references for the ship lengths
Starship Size Table - a list of starship sizes as given in several publications
Starship Sizes - some general thoughts about how to determine a ship's size
Thanks to Boris S. for compiling the sizes of some alien ships and to Alexander Hartmann, Chris Spinnler, Black Knight, Masaki Taniko, Masao Okazaki, Michael Swantak, Kristian Trigwell and The-Didact for some of the ship diagrams. A number of images from the Star Trek Fact Files have been provided by Neutral Zone Starship Database and The Guardian of Forever. Special thanks to Alice Orbán for preparing some of the images.
Fleet Charts @ Gilso Star Trek Schematics
Starship Recognition @ Star Trek Minutiae