Check this out:

Seventeen inches. If you’re able to hog both armrests, add about four inches. I’m not a big guy–no one ever says, “Mad Biologist, you need to drop twenty pounds.” I’m also a smidgen below average height, and shoulder-to-shoulder, I measure 22 inches. Seated on a chair, my maximum width (i.e., hip, thighs) is…seventeen inches. I barely fit. I have no idea how any six foot man, unless he is abnormally thin, is supposed to fit in a coach class seat. And these are international flights.

At some point, snakes will be the only things left on a plane….