The true length of the Akira class is not fully evident because of the following contradictory size figures (explained in the ship size table):

• Star Trek Encyclopedia II: 400-460m
• Star Trek Deep Space Nine Technical Manual: 464.43m
• VFX size according to a post (January 20, 1998) in alt.tv.star-trek.ds9 by David Stipes, VFX Supervisor DS9: 860' = 262.13m
• VFX size derived by Frank Gerratana: 340±10m

Analysis

VFX sizes The Akira class appears in "Star Trek: First Contact", various DS9 Dominion War episodes and VOY: "Message in a Bottle". A few scenes showing the Akira with ships of known sizes point to a length between 300m and 400m. It seems that this size has been consistently used. A possible reason is that, for the sake of simplicity, the same VFX sizes were nailed down for the three larger ships of "Star Trek: First Contact", although the Akira design should probably be longer than the Norway and the Steamrunner. This could be the reason why both the Steamrunner and the Akira in the image below are smaller than the Excelsior, yet, we can't be sure about the distances. Actually, most VFX scenes don't exclude the possibility the Akira is actually longer than 400m. "Message in a Bottle" shows the Akira next to the Defiant, whose size is in dispute as well and the evidence is even much more contradictory. Under the assumption that the Defiant is 170m, as always postulated, the Akira would be longer than 400m. If the Defiant is 120m, the Akira could be, but does not have to be smaller. For a more detailed analysis of Akira VFX shots, please refer to Frank Gerratana's Starfleet Ship Designs.



Structural analysis: The Akira class has countless windows - probably too many for an alleged warship - that allow an easy distinction of decks. There are 19 decks altogether, without the weapons pod. This yields an absolute minimum length of 330m, if the decks are only 2.5m tall and a maximum of 522m for an average deck height of 4m as on the Intrepid class. Assuming a standard deck height of 3.4m as on most other Federation starships seen so far the Akira would be 440m, and further evidence points to about the same length. There is no reason to assume that the Akira is an exception, even if we speculate that a warship might have decks of only 3m or less. The Defiant as the only warship so far is the best counter-evidence, at a generous length of 120m the decks (4-deck version, unless we ignore the MSD) would be 3.9m tall, not to mention the odd "official" ship with still 4 decks but 170m!



When we compare the top views of the Akira and the Sovereign classes, both from the Star Trek Encyclopedia II, it is obvious that the graphic artist took the same bridge modules as well as the same lifeboats for both drawings. In the lower left corner of the above image the Akira top view from this book is scaled to the Sovereign so that the two bridge modules are matched. The result is surprising, since the Akira would be only 272m long, much less than the minimum deck height allows, but about the same size that is allegedly used for VFX, according to David Stipes. However, the schematic in the Encyclopedia II definitely depicts a wrong bridge module, along with other minor flaws, such as a wrong color of the plasma (red instead of blue) in the nacelle window just behind the Bussard collector. It can be assumed that the images shown in Star Trek: The Magazine are much more precise, since they seem to be directly derived from the CGI, and they prove the Akira actually has a different bridge module. The lower right corner shows a comparison with matched escape pods, and the Akira turns out to be 440m as in the deck extraction. Therefore 440m±10m is the most likely design size.

Additional note: Alex Jaeger, the designer of the Akira, has been quoted that the saucer of the Akira is supposed to be (about) the same width as the Sovereign saucer, but this statement is not certain. If this is true, the length would be roughly 410m and therefore still in the above reasonable range.

Stipes' VFX size: David Stipes gives a length of only 262m in his newsgroup post. This is much too small for a ship with 19 decks. Actually, the decks would be only 2m tall! This is the main reason why this figure does not deserve further consideration, even if it holds true in part of the VFX shots.

Literature sizes: The first printed size comparison for the Akira is given in the Federation Starships chart in the Star Trek Encyclopedia II. Unfortunately, the ships are only roughly but not exactly shown to scale in this chart. Further explanations can be found on the ship size table page. Concerning the Akira, any length between 400m relative to the Intrepid (344m) or 460m relative to the Galaxy (641m) could be true. The faulty size charts remain unchanged in the extended Encyclopedia III.

The Deep Space Nine Technical Manual gives size figures for the ships featured in the series, including the Akira class. It can be noticed that several Starfleet as well as alien ships with definitely known design sizes are rendered too long in the DS9TM. The reason is that the size figures for the DS9TM were derived directly from the ship charts in the Encyclopedia II, by simply measuring the depictions and calculating the "real" lengths based on a 642.51m Galaxy or a 481m Vor'cha. Therefore the Akira size figure in the DS9TM is not new, but a consequence of the incorrect (or at least highly inaccurate) Encyclopedia II chart. The intended size for the chart is somewhere between 400m and 460m.
The VFX shots mostly suggest an Akira class of less than 400m length, but the ship could be larger if we take into account that the Akira is shown either too small or next to ships (in the same plane) that don't really allow a size comparison (Steamrunner, Defiant). The structural analysis points consistently to a size of 440m±10m. This is most probably the design size intended by Alex Jaeger. The Akira sizes given in the official literature are in the expected range, but not reliable because of careless scaling of the ship schematics. Unless the ship is shown at a really small size next to a ship whose size is definitely known, I will stick to the 440m Akira.
Thanks to Frank Gerratana for his analysis of VFX scenes involving the Akira class.