Universe Today shared a really great photo of the Ares I-X test launch vehicle that's currently being assembled at NASA's Vehicle Assembly Building. Ares I-X is really huge, comparable to the Saturn V, so it made me curious to see Ares being assembled in a stack that looked very similar to the dimensions of the Saturn V. The stack has been modified for use with Ares as you can see in the photo of Ares being assembled.
Compare that to a photo of the Apollo 4 Saturn V being assembled, it looks like Ares is being assembled in the exact same spot. It's a nice example of the changes that go on inside the VAB too, you can see all the new platforms that have been added over the years but that first shape of the Saturn V is still visible!
For reference, the Saturn V rocket was 110.6 meters tall (about 363 feet) and a whopping 10.1 meters (33 feet!) in diameter. Our new Ares rocket is just short of that number at 94 meters tall (310 feet). The Ares has two sections: the lower booster section containing the first stage is based off the shuttle solid rocket boosters which would indicate it has a diameter of 3.7 meters (12 feet) while the later stages in the larger portion are 5.5 meters (18 feet) in diameter.