Of kilometers and miles
Get ready to do some math in your head
Somewhat confusingly, the Brits use both miles and kilometers—though they're meant to be converting to the latter, metric measurement.
Road signs still use miles and yards (and speed limits are in miles per hour), but otherwise most measurements are supposed to be in metric.
Converting kilometers and miles
This conversion is easy enough to do in your head. A kilometer (km) is equal to 0.62 miles, and a mile is 1.61 km.
OK so it's not THAT easy. Still, doing a rough calc in your head isn't that hard. For kilometers to miles, just break it into two bits: 50% plus 10% (which totals 60%, or 0.60), then round up a smidge for that extra 2% (the 0.02).
That sounds more complicated than it is: Say you're looking to convert 80 km. OK, so to get 50% you just cut that in half, which is 40. Tuck that away in a crevice of your cerebellum for a moment.
Now take 10% of the original 80—which is 8—then add that to the 40 and you get 48. Round up "a smidge" to cover that extra 2% and you get 50. That means 80 km is roughly 50 miles (actually, it's 49.6, so close enough).
So if a road sign says the next town is 80km away, that's about 50 miles.
If your speedometer says you're going 120 kph, that means you're going way too fast (remember: slow and cautious). Ease off to 100 kph or less (about 60 mph).
Here, I'll make it easy for you with the table to the right.
Frankly, you'll rarely ever need to convert the other way, unless you want to say to someone in Europe something along the lines of "I live 20 miles outside of Boston," only put it in kilometers terms so he understands where your suburb is. No biggie. Ten miles is about 16 kilometers, so tell him you live 32 km from Boston. (This is assuming, of course, he has more than a vague sense of where Boston is in the first place.) That cheat sheet is to the right.