The Star Wars Databank concurs with the Death Star II being 160 kilometers in diameter, because that is the figure stated in the 1983 Return of the Jedi Sketchbook. The novelization of Return of the Jedi describes Death Star II as "almost twice as big" as the first Death Star but does not specify whether this applies to the volume or diameter. This contrasts the 900 km diameter figure stated in the Inside the Worlds of the Original Trilogy fact book. Curtis Saxton, author of the Episode II and III Incredible Cross Sections books, claims that the scaling with the Sanctuary Moon in Return of the Jedi also shows that the second Death Star was 900 kilometers in diameter. According to Star Wars Insider #69, page 23, DK nonfiction's assertions (which includes the book claiming the 900-kilometer diameter) is considered canon by Lucasfilm Limited. The level of canon was not revealed.
Lucas has made offhand comments regarding the first Death Star. He explains that the incomplete Death Star at the end of Revenge of the Sith was the exact same one as seen in A New Hope. He goes on to say that it would be "a bit of a stretch", but explains that due to "union disputes and supply problems", it took 19 years to build. However, Kevin J. Anderson's novels Jedi Search and Champions of the Force explain that a prototype Death Star was built in preparation of construction of the first Death Star in A New Hope, which would give another explanation for why the first Death Star took so long to build, in contrast with the second Death Star from Return of the Jedi. The contradiction between the novels by Kevin J. Anderson and the movies have since been resolved (or retconned) in The New Essential Chronology, which establishes that the first Death Star was indeed the one seen at the end of Revenge of the Sith: however, major problems with the technologies used to create the superlaser led to the creation of a testbed proof-of-concept prototype to ensure that the superlaser and the other systems would work. Created by Bevel Lemelisk and Tol Sivron, this is what became the Death Star Prototype. Once this was completed and tested successfully the First Death Star was completed, thus reconciling the various elements of continuity.