In a complete coincidence, a meteorite struck central Russia last night. It's estimated to be 15 meters or 49 feet before impact. That's the largest meteor to hit Earth since the one that crashed into Siberia in 1908.
To get a sense of scale, check out this image from BBC World:
That helps, but because I'm me I wanted to compare it to other asteroids. Fictional ones. And the first one I thought of is the rock that houses the space slug where the Millennium Falcon takes refuge from Imperial ships in The Empire Strikes Back.
Wookieepedia refers to the The Essential Guide to Alien Species and The Wildlife of Star Wars: A Field Guide and states that due to the lack of gravity, the specimens of exogorth living in the Hoth asteroid field were the largest of the species. The one the Millennium Falcon unwittingly flew into is a whopping 900 meters (2,952 feet) long. See, freaking gigantic.
We also know the the rock was one of the biggest in the asteroid field. Han says, "I'm going in closer to one of the big ones."
He's got a way with words.
Finally, we know from the Millennium Falcon Owner's Workshop Manual that the length of the ship is 34.37 meters (112.76 feet). That fact isn't going to really help prove anything in my example but hey, trivia!
I couldn't find a canonical source on the internet to get exact sizes for anything in the Hoth Asteroid Field, but an unofficial book by Jeanne Cavelos titled The Science of Star Wars compares the Hoth asteroid belt to a belt of asteroids that exists in our galaxy between the orbits of Mars and Jupiter. The book states:
"Of these millions [of asteroids] fewer than ten are larger than 200 miles across. A larger number, about 250, are over 60 miles across. Most are 1/2 mile or less across."Jumping back to Han saying the asteroid he chose is one of the largest, I estimate the asteroid is between 0.55 miles and 200 miles. How's that for a ridiculous range? I'll leave it for now, but I bet if I watch the film and slow it down to take screenshots I can use the known dimensions of the Millennium Falcon to get closer. For science. Or something approximating science.
Asteroid 2012 DA14 is 0.03 miles wide. The space slug asteroid is 0.55 - 200 miles wide. Slight difference. If a space slug asteroid comes anywhere near our planet, we're screwed. The end.