The size of the Edison class

The Edison-class was a type of Federation starship operated by Starfleet during the early 25th century. Based on the configuration of the Hoover class from the 23rd century, it contains many design elements of the ships from "Star Trek First Contact", especially the Saber class.

 According to this blueprint the ship has 20 decks.

schematic by Star Trek Online

• The premise for all my deck calculations: a deck is 2.5m + 0.5m for EPS cables, power cables, ... = 3m height for a deck. 
• My calculations follow a purely mathematical approach. I do not compare bridge modules or disk heights with each other. I always pull in decks based on the rows of windows and then calculate a physically plausible room height.

With a deck height of 3m, this results in a total length of 379.4m.
The official length is therefore correct. This is one of the few examples where the official length of the ship coincides with the mathematical "real" ones.

The size of the Pathfinder class

The Pathfinder class was a type of Federation starship that had entered service by the early 25th century. Many elements are reminiscent of the design of the earlier Intrepid-class of the 24th century like the USS Voyager NCC-74656. For example, there are the indented windows, the bridge module, the auxiliary deflector, impulse drives, the side sensor strips, the movable warp nacelles...

As with all my size calculations, I first spaced the decks evenly.

schematic by Star Trek Online

According to this blueprint the ship has 14 decks.

• The premise for all my deck calculations: a deck is 2.5m + 0.5m for EPS cables, power cables, ... = 3m height for a deck. 
• My calculations follow a purely mathematical approach. I do not compare bridge modules or disk heights with each other. I always pull in decks based on the rows of windows and then calculate a physically plausible room height.

With a deck height of 3m, this results in a total length of 340.1m.
The official length of 431.42m is therefore too large. If that were the case, a deck would have a height of 3.80m.

By the way: The official length of 431.42m is achieved if the Aero Shuttle (front lower saucer section) is scaled up to the same size as the one of the Intrepid class. This does give you huge decks, but it's a good example of how arbitrarily ship sizes are sometimes determined.

The size of the Enterprise-C

The USS Enterprise (NCC-1701-C) was a 24th century Federation Ambassador-class starship operated by Starfleet. It was the fourth Federation starship to bear the name Enterprise. In 2344, Captain Rachel Garrett served as the ship's commanding officer.

Not as much effort was put into the design of the Enterprise-C as was the case for the "stars" of Star Trek such as the Enterprise-D or -E. Therefore, there is only rudimentary information about the ship's construction, such as the drawings of the outer hull. As a first step in calculating the size, I added decks to the original blueprint of the Enterprise-C. 

Enterprise-C sketch by Rick Sternbach

According to this blueprint the ship has 37 decks.

• The premise for all my deck calculations: a deck is 2.5m + 0.5m for EPS cables, power cables, ... = 3m height for a deck. 
• My calculations follow a purely mathematical approach. I do not compare bridge modules or disk heights with each other. I always pull in decks based on the rows of windows and then calculate a physically plausible room height.

Now I checked whether this also matches the external appearance of the Enterprise-C in terms of the windows and the shuttle bays. The number of 37 decks fits this assumption very well.

With a deck height of 3m, this results in a total length of 491.5m.
The official length of 524.25m is therefore a bit too large. This is mainly because the producers issued the instruction that the Enterprise-C should simply have a length between the Enterprise-D and the Excelsior.

That's why Andrew Probert's initial design for the Enterprise-C was also included on the "old" size chart.

This size chart also contains the wrong size of the Excelsior class. If you just consider that the Excelsior class has 32 decks, then it already appears too small on the size chart.
 

The size of the Oberth class was also determined somewhat arbitrarily.

The size of the Enterprise-E

The USS Enterprise (NCC-1701-E) was a 24th century Federation Sovereign-class starship operated by Starfleet. This ship was the sixth Federation starship to bear the name Enterprise.

I never really considered the size of the Enterprise-E until I looked at the LCARS graphics on the Enterprise-E's MSD (Master Situation Display).

There I noticed that the silhouette didn't match the real one of the spaceship.  

So I traced the Tourbolift LCARS graphic and that of the bridge's MSD (which are identical).

screen used tourbolift LCARS grahic by "Star Trek Fact Files"

 According to this MSD the ship has 24 decks.

• The premise for all my deck calculations: a deck is 2.5m + 0.5m for EPS cables, power cables, ... = 3m height for a deck. 
• My calculations follow a purely mathematical approach. I do not compare bridge modules or disk heights with each other. I always pull in decks based on the rows of windows and then calculate a physically plausible room height.

And in fact, with this MSD, the total length of the spaceship is calculated to be 572.2m if one deck has a height of 3m.

A design sketch version was used to draw the decks that didn't correspond to the blueprints of the later model or the CGI Enterprise-E.

design sketch "The Art of John Eaves"

design sketch with MSD overlap

For the correct silhouette I used the CGI image from Santa Barbara Studios' CGI model of the Sovereign-class. (Star Trek: The Magazine Volume 3, Issue 11, page 50). 

Now I compared it with the silhouette of the spaceship. 

Without doing any calculations, it is immediately clear that the total length of the MSD can't be correct because the final blueprint wasn't used for the MSD.

If we now use the height of 3m for a deck, we calculate a total length of 718.8m for the Enterprise-E.
The official length of 685,8m is therefore wrong.
And one more thing: If you look closely at the side view of the Enterprise-E (the real one), it has 26 decks (and not just 24 decks, like in the MSD).

Only in this configuration would the main engineering on deck 16 and the upper shuttle bay in the correct position.

The configurations on the Enterprise-E for Star Trek Nemesis made it slightly shorter because the warp nacelles were raised a little and pushed forward by 3.5%.
Additional phaser strips and photon torpedo launchers have also been added.
In the end the extended saucer detail beside the upper Shuttle bay had no effect at all in the side view because it was too flat to be seen there. Nevertheless, this extended detail gives the appearance of the Enterprise-E a more smooth look.

 This results in a length of 706.1m for the Nemesis configuration.

The Size of the Excelsior II class

 The Excelsior II class was a Federation starship class that was in service with Starfleet by the early 25th century. In 2401, the USS Excelsior was amongst the fleet led by the USS Stargazer to meet a Borg faction. Cadet Elnor and Commander Raffaela Musiker were both assigned to the vessel which took part in protecting the quadrant from the massive energy released by the opening of a transwarp conduit by an unknown source.

• The premise for all my deck calculations: a deck is 2.5m + 0.5m for EPS cables, power cables, ... = 3m height for a deck. 
• My calculations follow a purely mathematical approach. I do not compare bridge modules or disk heights with each other. I always pull in decks based on the rows of windows and then calculate a physically plausible room height.

I have drawn decks based on the clearly visible screen opening of the bridge on deck 1. The ship was obviously designed in such a way that the number of decks is exactly based on the size of the bridge.

 

side view by Star Trek Online

 

The ship was marked with an official length of 588m.

 

With a height for each deck of 3m, the total length is 694.9m.  

If the ship were only 588m long, the decks would be 2.5m high, including the cables and technology. This would leave only 2m of headroom.

 

The original Excelsior class was also already calculated incorrectly. And this despite the fact that there was an Excelsior-MSD (Master Situation Display) with the decks.

The size of Timeship Relativity

The USS Relativity (NCV-474439-G) is a 29th century Federation Wells-class starship operated by Starfleet. The timeship was commissioned at the University of Copernicus, and was initially under the command of Captain Braxton.

• The premise for all my deck calculations: a deck is 2.5m + 0.5m for EPS cables, power cables, ... = 3m height for a deck. 
• My calculations follow a purely mathematical approach. I do not compare bridge modules or disk heights with each other. I always pull in decks based on the rows of windows and then calculate a physically plausible room height.

It's not so easy to see in the Star Trek Voyager episode, but the bridge of the USS Relativity has a large window structure on its ceiling.

image by Eaglemoss Collection

Using the high-resolution depiction of the USS Relativity in Eaglemoss magazine, you can draw the size of the decks in the side view and thus determine the length of the ship.

 

side view by Eaglemoss Collection

 Assuming a deck is 3m high, this gives a length of 263.7m for the USS Relativity.

The size of the Klingon Sarcophagus Ship

The Sarcophagus, or Ship of the Dead, was a Klingon starship that originally served as the command vessel of the House of T'Kuvma. In 2256, the Sarcophagus was encountered by the USS Shenzhou at the edge of Federation space.

The Set Designer David Moreau published a top view of the Sarcophagus ship's bridge. My calculations follow a purely mathematical approach. In this case I was able to use the correct dimensions from the bridge set.
On this you can see the dimensions of the opening of the front window (9'-6'' = 2.74m + 0.15m: overall 2.89m).

Sarcophagus ship bridge - by David Moreau

According to this set blueprint, the entire dome window has a diameter of 4.27m.
It is one of the largest bridge sets ever built for Star Trek. However, I had my doubts early on about the officially published length of the ship (2550.6m), because it seemed very gigantic (even for such a large bridge window).

This gives the entire spaceship a width of 472.7m.

 This results in a length of 993.06m for the Sarcophagus ship.