Metric basics
Don’t shoot the messenger here:
I’m not promoting metric,
I’m not advocating for metric,
I’m not saying metric is OK.
I just wanted to help those who are subjected to metric.
You can and should use a conversion app for when it really matters but this is just a rough guide for those who want some basics.
Distances
A meter is around a yard, more or less, so ten foot is around three meters. A meter was originally defined as one ten-thousandth of the distance between the equator to the pole, so 1/40000 of the Earth’s circumference. With the garbled measuring powers they had back then, that is not saying much.
Each kilometer is a thousand meters. Five kilometers is around three miles, and ten kilometers is around six miles. Going the other way, ten miles is a little over sixteen kilometers, which means that five miles is eight kilometers.
Going small, this is so dumb but we have both centimeters (one-hundredth of a meter) and millimeters (one-thousandth of a meter) and yes, confusion between those two have messed up many a project. Two inches are approximately five cm which is also fifty mm.
Sizes
100 mm is 10 cm which is 1 decimeter which is a tenth of a meter. A cube of that is a liter. A liter is more-or-less a quart, a fourth of gallon or two pints.
A cube of one centimeter is one milliliter (yes, this is dumb). Milli means one thousandth while kilo means thousand. A hundred milliliters is a deciliter, which is what we use instead of cups; it’s a li’l less than half a cup, two cups is almost five dl.
Weights
Now this is the good part: one liter of water weighs one kilogram, which is a little over two pounds, or a stone is a little more than six kilograms. So you can just double a kilogram weight to get an approximation of the pound weight. Why “kilogram” is the main unit and not a gram (a thousand grams are one kilogram) I’ve never understood. That’s just how it is.
But a good thing for all y’all gem lovers out there is that a carat is actually a metric-based unit already—five carats are exactly one gram.
Areas
These aren’t exactly day-to-day for me so I had to look it up. A hectare is an area that’s a 100 meters by a hundred meters. (Or 50 by 200 or any other weird shape just as long as it's that size.) Usually imperial units are a bit bigger like two cups is five dl, two inches is five cm but with hectare, it’s two hectare is close to five acres. I’ll try to remember that by thinking that “hectare” has more letters than “acre” just like “inch” has more letters than “cm” and “cups” has more letters than “dl”.
For things like apartment sizes it’s a li’l easier; use an app when it really matter down to the exact digit but just to get an overview, 100 square feet is a little more than nine square meters, so just lop off the last digit. When someone says “Oh I manage to live so minimalistically at 400 square feet” I can immediately know their place is way bigger than mine using the lop-off shortcut ("400 becomes 40"; it's actually 37.16 which isnclose enough).
Temperatures
Temperature… While there is a formula, it’s convoluted (multiply ˚C by nine, divide by five, then add 32, or the other way: subtract 32 from ˚F, then multiply by five, divide by nine) it’s probably best to just memorize some key values. Ice is 0˚ C, steam is 100˚ C, water is liquid in between. C is actually good for cooking for that reason. 0˚ C is 32˚ F, 37.78˚ C is 100˚ F, 100˚ C is 212˚ F. (Since 20✕9+32 = 212. All Celsius values that are cleanly divisible by five come out as integer Fahrenheit values.) Fahrenhet is good for weather. 0 is really cold outside and 100 is really hot outside. Celsius is cranked up to be about literally boiling things on the stove or in the lab, and it’s off by thirty.
So an increase by one degree ˚C is approximately 2˚ F; if it gets ten degrees hotter in ˚C that’s around it getting twenty degrees hotter in ˚F! Eighteen to be exact! The problem is that F has a 32 degree head start so for a super rough conversion from C to F: double and add thirty.
Learning a system
Conversion is no good if you wanna learn a system. For example, D&D uses imperial and my players came from metric so I was always discouraging converting to metric or refering to metric, instead always pointing to references like “oh, it’s around a foot” and holding up my hands approx a foot apart, or “ten by ten foot is like this room” or “OK, I’m five foot seven so on me the water would go up to here” or “it weighs like four swords”. To start thinking in the other system directly as soon as possible. I know that might sound like a mistake akin to “whole language instruction” but I think this is a different case.
And if you just need a one-off, there are apps for that. If you're a translator of fiction, remeber to round so your characters are saying reasonable things. No one says "OMG we're going over 160.93 mph!". If you're an engineer, of course never round and instead be super precise.
Rough conversion guides like this page is for the middle ground. When you’re subjected to metric more than a one-off but less than actually having to learn it, this page is for you.🎁
It’s for those who are metric-curious but not invested. Who still want to hate it but want to know a little bit about what they’re hating.
Phonics vs Whole Language Instruction
PS
Metric is also the name of a super good Canadian band that I really love! Waves is my favorite song of theirs among many many fantastic gems. But I can pretend that the band name means “a metric to measure by” as opposed to “the metric system”.
Source