Why don't all rulers measure in mm?

Answer by  quisqualis (1756)

In the US, people grow up with inches, rather than metric measurement. That makes us the exception to metric uniformity. Fortunately, most rulers made today (perhaps all of them) are dual metric and inch, so people have a choice. It is really time the US managed to switch over to metric.

Answer by  Travis404607 (3916)

There are rulers which have one side for inches, and one side for millimeters, you just have to know where to look. Most have inches and centimeters, though. Try a yardstick.