So you’re in the middle of the great conversation about this interesting, crazy story of how bitterly cold it was climbing to Base Camp of Mt. Everest, and you’re spitting out all these numbers, only to find a blank expression on your new friends’ eyes. Or you’re speeding by on a motorway and have no idea what the speed limit really is.
Ah, yes, miles and kilometers. Fahrenheit and celsius. Here’s a quick and dirty way to make quick calculations in your head while in the middle of something.
The official conversion rate we learned in high school is:
T(°C) = (T(°F) – 32) × 5/9
But nope, that’s not going to happen on the fly. So here’s a quicker (and not scientific) way.
F = C x 2 + 30
So, if someone says it was a scorching 38 degrees C, simply double it (76) and add 30 (106 F). It’s actually a few degrees less than that, but in my experience 102 and 106 feel very similar.
The opposite (thanks to good ‘ole Algebra) is C = 1/2(F – 30)
When you’re relating how your relatives are stuck in a snowstorm in New England, at around -10 degrees F, subtract 30 (-40) and divide by half (-20 C).
In school, we learned that 1 mile = 1.6 kilometers, and 1 kilometer = .62 miles.
When you’re on a motorway, it’s important to know the speed limit. Or else you might get pulled over (true story from my time in Ireland). For a while, my mom just tried to match the other cars’ speeds, but we thought that might not be the safest decision. So i pulled up a conversion table on my phone and I yelled out the mph whenever we passed a speed limit sign. Eventually, I got good enough I could get (more or less) and we made it through the entire country without a ticket.
Basically, when you’re converting from miles to kilometers, you’re adding 60%. When you’re doing the opposite (converting kilometers to miles), you’re subtracting around 40%. The easiest way to break it down is add/subtract by 50%, then add/subtract by 10% (or “a little bit extra”).
A speed limit sign proclaiming 80 means around 48 miles per hour. The actual conversion is 49.7 mph. M = (1/2K) + 10%
A tourist guide explaining the next town is 30 miles away is easily converted (for your international friends) to about 50 kilometers away. The real conversion is 48.2 kilometers. K = 2M – 10%.
1 kilo = 2.2 pounds.
This is probably the easiest conversion. To know your bag limit in kilos, basically, double a pound and add 20%. Or, if you’re in a real hurry, add “just a little extra.”
10 kilos becomes 22 pounds.
50 pounds becomes 22 kilos.
Stones (for anyone traveling to the UK) are a little different:
1 stone = 14 pounds = 6ish kilos.
I’m pretty sure you can do the rest of the math on your own.