Apartments in Chile - as in much of the rest of the world - are measured in square meters. However, in the US, they are measured in square feet. Since people get really used to the meanings of various measurements, seeing (or hearing) the same thing measured in different units provokes a different response (or sometimes just a sense of puzzlement).
One such measurement is living area. In Ann Arbor, I lived in a ~800 sq. ft., single-room cabin in the woods. To others who use square feet to designate living area, this has an intrinsic "feel" to it. To people in Chile (and much of the rest of the world), this means ... not much.
Sure, you can make quick back-of-the-envelope calculations to say, "Well, 3 feet is roughly 1 meter," but that fails (utterly) to account for squaring. Without a quick-and-dirty conversion factor, in order for Chileans to understand how big that cabin was, they'd have to take the square root of 800 (28.284) and then divide it by 3 (9.428) and then square it (88.888), which is kind of difficult to do on the fly.
However, there is an easier way. Using the handy site, onlineconversion.com, one can find that 1 square meter is equal to 10.763910417 square feet. To change this to a handy back-of-the-envelope conversion factor, just multiply square meters by 11 or divide square feet by 11 (a handy trick might be to multiply square feet by 9 and then divide by 100).
Ergo: My 800 square-foot cabin in the woods is roughly (9*800)/100) = 72 square meters (plus a bit). The actual answer is closer to 74 square meters, but this conversion is far easier (and far more accurate) than the one presented above.