It is also, according to a new calculation published in the journal Surgical Technology International, the amount of force exerted on the head of an adult human who is looking down at her phone.
Kenneth Hansraj, a New York back surgeon, found this figure using a computer model of a human spine. An average human head weighs about 10 to 12 pounds, and tilting it down to check Facebook, send a text, or to Google the weight of an a human head increases the gravitational pull on said cranium.
"As the head tilts forward the forces seen by the neck surges to 27 pounds at 15 degrees, 40 pounds at 30 degrees, 49 pounds at 45 degrees and 60 pounds at 60 degrees," Hansraj writes in the paper.
According to Nielsen, Americans spend about an hour on their smartphones each day. Unless you train yourself to stare straight ahead into your iPhone screen, you could be continually stressing your spine. "These stresses," Hansraj writes, "may lead to early wear, tear, degeneration, and possibly surgeries."
Of course, physical therapists have been howling about the scourge of "Text Neck" for years. But it's certainly eyebrow-raising to learn that looking at Twitter in the supermarket checkout line is the equivalent of giving an aardvark a piggy-back ride.
Time to get Google Glass? Until, that is, scientists find that the device is crushing the nose-bridges of America.