The size of the Excelsior Class

The Excelsior-class was a type of Federation starship used by Starfleet from the late 23rd century through the late 24th century. As a long-range research vessel, it was the backbone of Starfleet for nearly a century, making it one of the fleet's longest-serving spaceship designs. The Excelsior-class was later replaced by the Sovereign-class.

• 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.

If you consider two decks for the outer part of the saucer (deck 7 + 8), the result is a perfect division of the decks for the whole ship. This gives the height of the neck to the main body an even number of decks.

schematic by TheLightWorks

The large MSD (Master Systems Display) from the background of the Excelsior class bridge also gives the number of decks that I calculated: 32.

Doug Drexler with his MSD of the Enterprise-B (artstation.com)

MSD Enterprise-B by Doug Drexler (artstation.com)

Incidentally, this division also corresponds exactly with the additional construction on the main body of the Excelsior Refit (USS Enterprise-B). The place where the Nexus energy ribbon hits the Enterprise-B and thereby pulls Captain Kirk into the Nexus is exactly two decks high.

screencapture by trekcore.com (Star Trek: Generations)

According to Andrew Probert's size chart (he extended the ILM chart for Star Trek: The Next Generation, sizing his Ambassador concept halfway between the Excelsior and the Galaxy class), the official length of the ship is 467m (1531 ft). If you pull decks into the side view of the spaceship, this size seems a bit too small. 

ILM Size Chart by Andrew Probert

Commented on this by Bill George of ILM:

"The only description we had at the time was that it was "souped-up" and bigger than the Enterprise. The size the miniature was built to was determined by the camera guys as being the optimal size to shoot. As I recall Nilo [Rodis-Jamero] did that size comparison chart, but it wasn't necessarily followed. The issue of true scale wasn't a consideration. Budget, ease of use, art direction and dramatic intent were what influenced the construction of the ship."

After calculating the decks, this results in a length of 606.9m.

If the Excelsior class were 467m long, then its decks would be only 2.3m high (inclusive 0.5m for EPS cables, power cables, ...). Then only 1.80 m remained for the clear height of the rooms.

The size of 606.9m corresponds much more to what can be seen optically in the Star Trek series:

screencap TNG:
"Encounter at Farpoint" 

by trekcore.com

screencap TNG: "The Child"
by trekcore.com

screencap DS9: "Favor the Bold" 

by trekcore.com

screencap DS9: "Paradise Lost" 

by trekcore.com