I really don't want to turn this into another ship size argument, but the Kelvin saucer is about twice the width of the old 1701's. The engineering hull is a little bit bigger than the TMP Enterprise. Overall it's TMP Enterprise - 1000', Kelvin - 1500'. Yes I was sad enough to make a size-comparison chart when everyone was freaking about the ship size numbers released 
All the ships in the fleet to Vulcan were Kelvin kitbashes, and they all looked to have saucers the same size as the new Monsterprise.
Remember it had to fit 800+ crew and 47+ shuttles too.
(gently places can of worms in hole and starts burying)

All the ships in the fleet to Vulcan were Kelvin kitbashes, and they all looked to have saucers the same size as the new Monsterprise.
Remember it had to fit 800+ crew and 47+ shuttles too.
(gently places can of worms in hole and starts burying)