How big is the Rosetta comet?

Rico's friend Kelley forwards this TechnoBuffalo article by Brandon Russell about the impending comet:

That comet that Rosetta finally met up with after ten years of traveling doesn’t look so scary, right? Just a coarse space rock, nothing special. In actuality, the thing is scary huge. You see that teensy little city in the comet’s shadow (illustration at bottom)? That’s (we think) Los Angeles. It, along with the surrounding areas, would be completely wiped out if 67P/CG managed to hit Earth.
Do you appreciate its size now? The European Space Agency’s Rosetta satellite snapped the photo at top after approaching the massive comet, which is estimated to be about three kilometers wide. You can easily walk three kilometers in about an hour, give or take. But put that into perspective of a space rock that’s traveling at thousands of miles per hour, and it becomes a lot more frightening.
The purpose of Rosetta’s long mission is to study one of these beasts up close, and observe how the comet changes as it crosses the sun’s path. The ESA plans to try and land a probe being carried by Rosetta onto comet 67P/CG this november, which will then drill into the rock’s surface. The hope is that scientists will get a better understand about the origin and evolution of our solar system.

Rico says that, of course, if one like this ever does land on Earth, it's lights-out for life on the planet, folks...