Page 72 of
Before the Storm, Chapter5 (Guild Books America collected trilogy hardcover edition):
"The New Republic is a mutual self-protection pact among four hundred sentient species, and an economic partnership between eleven thousand inhabited worlds," said Leia. "But you'll find that the autonomy of member worlds is hardly compromised at all -- "
Elsewhere in the same novel, President Organa Solo states (p. 22) that there are ten new applications for membership per day; earlier in her conversation with Viceroy Spaar, she mentions (p. 72) "the leaders of some of the hundred worlds which have become members in the last twenty-eight days."
The New Republic comprises, at this time, approximately 1.1 per cent. the territory of the Galactic Empire at the time of the Battle of Yavin, if one counts only the one million full members of the latter, and disregards the fifty millions of governments, protectorates, and colonies also controlled by the Empire.
Given that the Empire had an average of 0.025 Star Destroyers per member, one could reasonably expect something on the order of 275 Star Destroyers' worth of warmaking capacity on the part of the New Republic, if the New Republic maintained similar levels of operational readiness.
Of course, one must consider that whilst this New Republic is nominally and ideologically identical to the New Republic of the pre-Operation Shadow Hand period, it is not actually so. That New Republic was handily dismantled by the Galactic Emperor when he emerged from the Deep Core in
Dark Empire; in fact, by the time of
Empire's End, one can conclude that the Empire had already seized control of almost the entirety of its former domains. (For documentation of this shift in territorial dominion, refer to
Heir to the Empire,
Dark Force Rising,
The Last Command, the
Dark Empire Sourcebook, and
The Essential Chronology.)
The New Republic seen in the Black Fleet Crisis has only been re-constituted six years previously; prior to that, it was once again the rebel Alliance, having lost the majority of its territory and conventional warmaking capacity. Considering how easily and thoroughly the New Republic was defeated, it is not at all surprising that its second incarnation does not boast of the same rapid growth and territorial expansion as its first.
As a side note, one finds that the Fifth Fleet is treated somewhat oddly throughout
Before the Storm; when it is first introduced (p. 11), the narrator refers to it as the "Fifth Battle Group of the New Republic Defence Fleet." In the Headquarters, New Republic Defence Forces, the members of the Senate's Council on the Common Defence and the Joint Operations Defence Staff refer to it (p. 22) as the "Fifth Fleet."
Finally, when General A'baht sends a dispatch to the HQ, NRDF, recommending that his command be considered operational, he refers to it (p. 24) as the "Fifth Defence Task Force."
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