You can always look at what they got at the Apple Airport Extreme N page which is somewhat limited. Or you could look at the great photos that AppleInsider has posted.
Here are a few shots of the box. It is about 2-1/2 inches thick and 8 x 8 inches square. That's the box. I like the economy there.
Box Top Showing the Airport Extreme N front
Box Bottom Showing the Airport Extreme N back
Airport Extreme N Box Label -- including all the specs
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