Measurement and Conversion
Chapter 6: Measurement and Conversion
In 1791, the French Academy of Sciences defined the meter (or metre, as much of the world spells it) as one ten-millionth of the distance from the equator to the north pole through Paris. In 1983, the General Conference on Weights and Measures redefined the meter as the length of the path travelled by light in vacuum during a time interval of
of a second. You’ll surely sleep better at night for knowing.
So whether you prefer meter or metre, it’s still the same thing. It’s just a little more than a yard long (1 meter ≈ 39.37 inches — see the following section).
That little squiggle (≈) means approximately. That’s about the height of a parking meter on a city street, but that has nothing to do how the meter was named. Sources say the word is from Greek, meaning a measure.
For a long time, the metric temperature scale was called the centigrade scale — with water freezing at 0 degrees centigrade and boiling at 100. Then they named it after Anders Celsius, a Swedish astronomer. But this system didn’t account for absolute zero — the lowest temperature theoretically possible — so now 0 kelvin (0 K) is defined as –273.15 degrees Celsius, or absolute 0. However, when you drive by a bank with an electric sign, you see degrees Fahrenheit (the American temperature unit) and degrees Celsius, but not kelvin.
In time measurement, a second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
The big advantage in using metric units (aside from most of the world using them) is that most of the conversions are multiples of 10. Now is that easy math, or what?
The American system
The United States is the only industrialized nation that doesn’t use metric for standard activities. Burma (Myanmar), Liberia, and the U.S. are the only coun- tries that haven’t adopted metric. Instead, the U.S. uses the American system.
The American system is sometimes called the English system, or its units are called English units. It dates back to colonial days. In the United Kingdom, on the other hand, the English system evolved to become the imperial system (see the section on the imperial system later in this chapter). The American system is similar, but not identical, to the imperial system.
Table 6-1 shows you how American units roughly compare to metric units.
They aren’t exact matches, but you can see which American units have simi- lar metric counterparts.
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Table 6-1 Comparing Main American and Main Metric Units
American Metric Length
millimeter
inch centimeter (2.54 inches)
foot (12 inches)
yard (3 feet) meter (39.37 inches)
rod (16.5 feet) furlong ( mile)
mile (5,280 feet) kilometer (0.6214 miles)
Area
square inch square centimeter (0.1550 square
inches)
square foot (144 square inches) square decimeter (0.1076 square feet) square yard (9 square feet)
acre (43,560 square feet) hectare (10,000 square meters, 0.01 square kilometers, 0.4047 acres) square mile (640 acres) square kilometer (0.3861 square miles) Volume
cubic millimeter
cubic inch cubic centimeter (0.0610 cubic inches)
cubic foot (1,728 cubic inches) cubic meter (0.0283 cubic feet) cubic yard (27 cubic feet) cubic meter (0.7645 cubic yards) Weight
gram grain
dram (27.3438 grains)
ounce (437.5 grains) gram (28.35 grams)
pound (16 ounces, 7,000 grains) gram (454 grams) kilogram (1,000 grams) hundredweight (100 pounds)
ton (20 hundred weight, 2,000 pounds) tonne (1,000 kilograms, 1.1023 tons) long hundredweight (112 pounds)
long ton (20 long hundredweight, 2,240 pounds)
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Chapter 6: Measurement and Conversion
American Metric Liquid volume
milliliter fluid ounce (29.5735 milliliters)
cup (8 fluid ounces) milliliters (237 milliters) pint (16 fluid ounces)
liter (1,000 milliliters) quart (32 fluid ounces, 2 pints) liter (1.0567 quarts) gallon (4 quarts)
Temperature
degrees Fahrenheit degrees kelvin
The American pound is also known as avoirdupois weight, as opposed to the troy pound (see “Troy weight: Just for bullets and bullion”) or the apothecaries’
pound (see “Apothecaries’ system: Not a grain of value any more” in this chap- ter). The key to distinguishing the American weight unit is that avoirdupois has 16 ounces in 1 pound. The others don’t.
For information on how to convert between the metric and American systems, see “Converting Length, Weight, and Volume” later in this chapter.
The imperial system, or the modern English system
The imperial system and imperial units are still common in the United Kingdom, which transitioned to the metric system legally in 1995 but still has many imperial units in use.
The U.K. Department for Business, Innovation and Skills decrees that draft beer and cider must be sold in pints or half pints. (However, gin, rum, whiskey, and vodka should be in sold in multiples of 25 or 35 milliliters and glasses of wine in 125 milliliter portions.)
Road sign distances and speed limits have to be expressed as imperial units.
You find similar situations in Ireland and Canada, where people are permitted or even required to use some imperial units. You also find some imperial units in use in former British territories: Australia, India, Malaysia, New Zealand, South Africa, and Hong Kong.
Just remember that many but not all American units are identical to imperial units.
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Troy weight: Just for bullets and bullion
Troy weight is a system for measuring weight (mass). It’s still very much alive, but it’s used mainly for weighting precious metals and reloading rifle and pistol cartridges. Its units are
✓ Grain
✓ Pennyweight
✓ Ounce troy
✓ Pound troy
The unit grain is the same in avoirdupois, troy, and apothecaries’ weight.
Propellant (powder) for firearms is still weighed in grains but is sold by the avoirdupois pound. Bullets are identified by their weight in grains but are sold in packages with a specific quantity.
Unlike the American avoirdupois pound, which has 16 ounces, troy weight has 12 ounces to its pound. It’s a smaller pound than an avoirdupois pound.
A carat is a unit of weight for a gemstone. It is equivalent to 200 milligrams (mg) or gram (g). Also, in the world of jewelry, you can divide a carat into 100 points. So, if someone gives you a 5-point diamond, there has to be a lot of love, because there isn’t much diamond.
Don’t get carat confused with karat (k), which is a measure of the purity of gold or silver, as in 14-karat gold.
Apothecaries’ system: Not a grain of value any more
Apothecaries’ weight is very similar to troy weight (the grain and the pound are the same, with each kind of pound containing 5,760 grains) and is rarely used. It is an old system for apothacaries (pharmacists) and scientists.
The units of the apothecaries’ system are:
✓ Grain
✓ Scruple
✓ Dram
✓ Ounce apothecaries
✓ Pound apothecaries
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Chapter 6: Measurement and Conversion
Apothecaries’ grains are still used occasionally in medical prescriptions.
Although most dosages are in milligrams (mg), some items may still be sold in grains (gr).
A pound apothecaries has 12 ounces. It’s a smaller pound than an avoirdupois (American) pound, which has 16 ounces, but the same weight as a pound troy.
Other legitimate but specialized measurements
As long as there are many things to measure, there will be many units of measurement. Over the centuries, systems developed as the trades or sci- ence required them.
Some of these systems seem to be passing into obsolescence, but as the world changes and technology evolves, new systems come into existence:
✓ Writing paper: In the world of the printing press, the following units evolved:
• Sheet
• Quire
• Ream
• Bundle
• Bale
You often buy printer paper at the office supply store by the ream. If you buy a case of ten reams, you’ve also bought a bale.
✓ Light-years and parsecs: In the world of astronomy, you measure large distances, such as the distances to stars. A light-year is the distance that light travels in a year. And since light travels very fast (299,792,458 meters