From The Romulan Empire - The Scimitar, one of the featurettes on the Star Trek Nemesis DVD:
Well the Scimitar is a ship that's about three times larger than the Enterprise, and the Enterprise is the largest Enterprise the Federation has ever made.Enterprise-E: 685 meters, 24/29 decks (depending which movie you watch, 29 in Nemesis
Enterprise-D: 641 meters, 42 decks.
And Herman Zimmerman has been with Trek for ages...
