Metric and Imperial equivalents

Most countries in the world now use the metric or SI system. The old British imperial system of weights and measures survives, in various forms, in the United States, United Kingdom, Canada, and Liberia, to greater or lesser extents and Myanmar still ploughs its own furrow, but in all these countries, except for the US, the metric system is widely understood. In the US, you'll find the metric system only used in scientific or military contexts, while in the UK and Canada, usage is more mixed. In scientific usage, the metric system is used exclusively in all countries of the world.

Some countries that are officially metric use non-standard units in everyday speech. While most of them are "metricised" (e.g. a German "Pfund" or pound being exactly 500 grams or half a kilogram or a Dutch ons being exactly 100 gram) some are not and the vague definitions of what exactly is meant by a "pound" or a "vara" (a Latin American unit of distance, somewhere between 0.5 and 1 meter, and sometimes weight) give you a sense of the confusion that led to the introduction of the metric system in the first place. Some special uses still apply non-metric units almost globally such as inches for bike-sizes or TV-sets or feet in aviation, although these are probably the only ones of interest to the average traveler.

To get by in countries that use a different system than you're used to, it's helpful to know some rough equivalents. We use "=" signs below, but some are approximations.

Temperature

A Celsius poem

Zero is freezing
10 is not
20 is warm
and 30 is hot

frigid freezing cold cool mild warm hot swelter cooked
°C  -40 -18 -4 0 4 7 10 13 15 18 21 24 26 30 32 35 40
°F  -40 0 25 32 40 45 50 55 60 65 70 75 80 85 90 95 104

Comparisons

 100°C  =  212°F  =  Water boils
  58°C  =  136°F  =  Highest temperature recorded on Earth
  37°C  =   98.6°F =  Human body temperature
  20°C  =   68°F  =  Room temperature
   0°C  =   32°F  =  Water freezes
 -18°C  =    0°F  =  
 -40°C  =  -40°F  =  Forty below zero!
 -89°C  = -129°F  =  Lowest temperature recorded on earth
-273°C  = -459°F  =  Absolute zero

To convert Metric (Celsius) to Fahrenheit, double the number and add 30. To convert Fahrenheit to Celsius, subtract 30 and divide in half. Close enough for most everyday applications. For scientific use

Fahrenheit = {(} C \times {1.8} {)} + {32}


Celsius = { {(} F - {32} {)} \over {1.8} }




Length and distance

Comparisons

Weight

For China, the jin (斤) is almost exactly 500 grams. In Germany the pound (Pfund) nowadays refers to a weight of exactly 500g.

Surface area

For small things, one might use square inches or square centimeters. There are about 6.5cm2 in one in2.

For floor area of an apartment, there are about 11 square feet in one square meter.

For large areas, there are about 2.5 acres in one hectare.

Comparisons

Volume

The standard metric unit of volume is the liter.

Many things, however, are measured in mL (milliliters) or equivalently in cc (cubic centimeters). Roughly, a teaspoon is 5mL and a fluid ounce is 30mL.

In both the US and Imperial systems, 4 quarts = 1 gallon and 2 pints = 1 quart. However, the US units are smaller than Imperial counterparts. A US quart is 32 fluid ounces while Imperial is 40; a liter is in between at 35. A US gallon is 128 ounces or 3.78 liters, while an Imperial gallon is 160 ounces or 4.54 liters.

For car and motorcycle engines, displacement might be given in cc or liters or cubic inches. 1000cc or one liter is 61 cubic inches.

Comparisons

Metric units

1mm = 1/1000th meter

1mg = 1/1000th g

1mL = 1/1000th liter

1cm = 1/100th meter

1km = 1000 meters

1kg = 1000 grams

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