First, let me say that there must be two different sizes, because in ST III the Constitution Class fit through the doors (at 141m wide), but a ship much wider would not. In TNG, however, the Galaxy Class Enterprise fit through those doors, and its 560m wide.
So, I get out my trusty ruler and the copy of ST:The Magazine with a good picture of Spacedock.
It shows the smaller one, as a Constitution Class vessel is in the doorway.
Said ship is exactly 10mm across the saucer, so our scale is 10mm=140m or so. Ignoring the antennae at both ends, the top of the highest dome to the bottom of the station proper is .... 303mm which scales out to 4242m.
The larger one would be ... larger. I'd say at least 4 times as big, which would be 16,968m.
That's issue #9 if you want the pic.
------------------
You're a Starfleet Officer. "Weird" is part of the job.