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Metric Conversion for Maniacs

The United States is one of the last countries on Earth that hasn't adopted the metric system. This adds one more complication for American travelers. The following guide is purposely incomplete and imprecise. Instead it is intended to give travelers a feel for commonly encountered metric units.

Time:

  • All times are the same in the metric system!

Length (and speed):

  • Medium lengths: a meter (m) is about 10% bigger than a yard. If I'm not worried about precision, I'll call a meter a yard and be done with it.  If I want to do better, I usually convert to feet and add the 10%. For example, a 3,000 m mountain would be 3 x 3,000 = 9,000', plus 900' (10%) or about 9,900' (the correct answer is 9,812.5').
  • Long lengths: on the highway everything is in kilometers (km). 1 km = 1,000 m (a thousand meters). From the meter conversion, we know this is about 3,300', but that's not very helpful for highway distances or speeds. An easier, but rough conversion is that 1 km is about half a mile. Slightly more accurate is 1 km = 0.6 miles. This is actually pretty handy because it says that 100 km is about 60 miles and 100 km/hour is about 60 mph. A common speed through towns is 40 km/hour, which is about 25 mph.
  • Small lengths: sometimes smaller units come up.  The most common for everyday use is the centimeter (cm). 1 cm = 0.01 m (one hundredth of a meter). Entertainingly, an inch is defined in terms of centimeters (1" = 2.54 cm exactly!). That makes 1 cm a little larger than 3/8". The next metric size down is the millimeter (mm), which is one tenth of a centimeter or one thousandth of a meter. That means that 1 mm is a little larger than 1/32". You can see that micrometers (one millionth of a meter) and nanometers (one billionth of a meter) are way too small to worry about.

Weight:

  • Medium weights: a kilogram (kg) or kilo is about 10% larger than two pounds. (Technically, a pound measures weight while a kilogram measures mass, but as long as you don't go into space, you can get away with assuming they're both measuring weight.) In the markets, you might see a price for half a kilo of tomatoes. That's essentially the price per pound. This is sometimes given as the price for 500 grams (see the next bullet).
  • Small weights: a gram (g) is 0.001 kilograms (one thousandth of a kilo). In markets, you will often see produce priced in units of 100 g or 500 g. Since there are about 28 g/oz, 100 g is a little less than 4 oz (or a quarter pound) and 500 g is a little more than a pound.
  • Big weights: there is a metric ton, which is 1,000 kg. That means that a standard ton is 2,000 pounds, a metric ton is 2,200 pounds, and a long ton is 2,400 pounds. Unless you're in the business, they are all close enough to not worry about the differences.

Volume:

  • Medium volumes: buying gas overseas is tough because it involves two conversions (gallons to liters and the local currency to dollars). The gallons part isn't too hard though. Americans are used to buying soft drinks and hard liquor in liter bottles, so they know 1 liter (l) is about a quart. If you want to be a little more accurate, a liter is about 5% bigger than a quart, so a gallon is about 3.8 l. When I'm buying gas overseas, I usually just assume four liters per gallon because uncertainty in the exchange rate (due to fees, etc.) make the whole transaction problematic anyway.
  • Small volumes: you'll sometimes see volumes listed as cubic centimeters (cc). 1 cc = 0.001 l (one thousandth of a liter or 1 milliliter (ml)). 5 cc is about one teaspoon or 15 cc is about one tablespoon.

Temperature:

  • Temperature is hard because of the offset. Most conversions don't have this problem. That is, zero kilometers is zero miles, zero liters is zero quarts, etc. Metric temperature is in degrees Centigrade (C). Unfortunately, 0 degrees C = 32 degrees Fahrenheit (F), which makes everything much less intuitive. Since centigrade is designed to be 0 at the freezing point of water and 100 at the boiling point, the formula is: degrees F = degrees C x 9/5 + 32. However, since converting temperatures in my head is laborious, I get by remembering the conversion at several key temperatures: 

Converting temperatures is tricky.

For the dieter:

  • If you're watching your weight, you are probably watching your calories, which is essentially the energy available in the food you eat. If you go to a grocery store overseas, they don't use calories though. Instead you'll find foods marked in kilo-Joules (kJ). (On American packaging, what's listed as a calorie is actually a kilo-calorie or a thousand calories--otherwise, most of us would be eating over a million calories a day and who needs that!) If you just divide the number of kilo-Joules by four, you will come close to the number of calories you are used to seeing on food in the United States. For example, if a meal is 1000 kJ, it's a little less than 250 calories.