I consider myself pretty conversant in metric units. I know that 20 kilograms is 44 pounds (double it and add 10%) and that five kilometers is a little over three miles (I’ve, uh, run a lot of 5Ks).

Katie has a PhD in maths, specializing in the intersection of dynamical systems and number theory. She reports on topics from maths and history to society and animals. Katie has a PhD in maths, ...

Every once in a while, you may see a temperature in Celsius instead of Fahrenheit. Your car thermometer may revert to the wrong system and you don’t know how to change it, for example. Since almost ...

Oh, America. You do so confuse the rest of the world, with your “pounds per square inch” and “cups”, instead of sensible measurements like Pascals and liters. And part and parcel of that is your ...