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Scott has a Ph.D. in electrical engineering and has taught a variety of college-level engineering, math and science courses.
Are you ready for an enlightening quiz?
Question: How many countries in the world have not officially switched to the SI (International System of Units), or modern metric system?
Answer: Three - The U.S., Liberia, and Burma.
Here's a map that answers this question visually, just to drive the point home (countries in red are not officially on the SI):
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The United States still uses a system called the U.S. Customary System, which is based on the English system of measurement. Over the last 200 years, nearly every other nation of the world has officially adopted SI. Even Great Britain has switched, with a few exceptions. In addition, the scientific world, as well as trade and commerce, uses the metric system, even in the U.S.
The English system of measurement had a good run, but there are a number of disadvantages of this system that we will explore in this lesson.
What is the English system of measurement? It is a system of weights and measures that evolved over time and was once the de facto standard throughout much of the world. The best definition of this system comes with the British Weights and Measures Act of 1824. This act defined a standardized set of measures for the British Empire, known as the Imperial Units. Here is a table listing several examples of these:
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The complete history of the English system of measurement spans many centuries. Countless books and articles have been written about this subject, and only a small fraction of the information will be summarized here. We'll be focusing on a few of the more interesting cases.
First, length. These units go back to the early Romans who settled in Britain. They defined a 'mille,' which means '1,000' in Latin, as a distance of 1,000 paces of two steps each. At about 5 feet per double-pace, a 'mille' became known as a 'mile' and was equal to 5,000 feet. The Romans were also fond of dividing things by 12, so a 12th of a foot in Latin was an 'uncia,' which later became the 'inch.'
Some of the English units of length came about by decree. For example, there is a legend that King Henry I, who ruled from 1100 to 1135, announced that a yard would be defined as the distance from the tip of his nose to the end of his thumb. In the latter part of the 16th century, Queen Elizabeth I decreed that a mile would be exactly 8 furlongs (a furlong was 660 feet), which works out to be 5,280 feet. This replaced the previous 5,000-foot mile.
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Next, let's look at weight. One of the most interesting histories is that of the stone. Dating to Babylonian times (2000 BCE), stones were used as a counterbalance on scales to weigh commodities. Here is a picture of a Roman stone dating to the second century AD:
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In the early history of the British Isles, stone weights were used extensively but varied in value from Scotland to Ireland to England and even county by county. The stone measure also varied by what was being weighed. For example, a stone of wool might weigh 14 pounds, but a stone of glass might be 5 pounds. Finally, in 1824, the stone was defined as exactly 14 pounds.
Finally, let's discuss volume. The British gallon was precisely defined by the 1824 Act as: '…equal in volume to 10 pounds avoirdupois of distilled water weighed at 62 degrees Fahrenheit with the barometer at 30 inches, or 277.274 cubic inches.' But it was not always this way. The first dry gallon was described by Edward I in 1303 as eight pounds of wheat. This led to wide-ranging interpretations and lack of standardization. Finally, Parliament, in 1696, defined a dry gallon to be a cylinder 18.5 inches in diameter and 8 inches deep. The dry gallon was also called the 'Winchester bushel.' They defined a liquid gallon, also called a 'corn gallon,' to be 268.8 cubic inches, which was exactly 1/8th of the dry gallon.
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For any of you familiar with SI, you probably know that the English system of measurements holds few advantages. So why hasn't the U.S. converted? The primary advantage to hanging on to the English system is cost of conversion. For example, in 2009, NASA stated that the conversion of the space shuttle program to SI would cost $370 million. This was a price tag for which NASA simply did not have the funds. In another example, when Great Britain began to process for metrification in the 1990s, the estimated cost for changing all of its road signs was the equivalent of between $1.5 and $1.8 billion.
The second advantage of continuing with the English system is customary usage. For example, distances in football and baseball are closely linked to feet and yards, and decades of records are kept in these units. Cooking is another area where customary units in the U.S. are quarts, cups, ounces, pounds, etc. Finally, our culture is filled with sayings, such as, 'Give him an inch and he'll take a mile.' It just isn't the same to say, 'Give him 2.54 centimeters and he'll take 1.61 kilometers.'
The primary disadvantage of the English system of measurement is converting from one unit to another. It's not easy to go from feet to miles, pounds to ounces, or gallons to pints. A common example is trying to remember that a square mile is 640 acres. The SI, on the other hand, is based on powers of 10, so 1,000 meters is a kilometer, 100 centimeters is a meter, 1,000 grams is a kilogram, etc. Conversion can often be done in one's head.
Another disadvantage of the English system is that the measures have not evolved in a systematic way. Most are arbitrary definitions that have their roots in hundreds or even thousands of years of tradition. The British Weights and Measures Act of 1824 did not necessarily correct this; it only sought to eliminate much of the variety in similar measures in use throughout the United Kingdom. Related to this disadvantage is the fact that there are so many different measures for length, weight, area, and volume to remember. In the SI, for example, there is just one primary base measure for length, volume, and mass/weight:
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The final disadvantage to continued use of a system based on the English system is that most of the world is on SI. In fact, SI is the universal international system for science, engineering, finance, commerce, and technology. It is increasingly difficult for countries not officially on the SI to stay competitive.
The English system of measures is a collection of measures for length, volume, weight, area, etc. that have their roots in hundreds of years of history. They were standardized somewhat by the British Weights and Measures Act of 1824, which defined the Imperial Units to be used throughout the British Empire. The history of these units is colorful, including heavy influence from the Romans and decrees by British monarchs.
There are a number of disadvantages to the English system, foremost of which is the difficulty in converting from one unit to another. Other disadvantages include the lack of a systematic foundation to the measures, the number of base measures to remember, and the fact that most of the world is officially on the International System of Units (SI, or the modern metric system).
The main advantage to not converting from the English system, or a system that is similar, is cost of conversion. A secondary reason for not converting is that a culture, such as in the U.S., can be rooted in the customary usage of feet, yards, quarts, miles, etc.
Although a few of the English measures are still used in Britain today, the country has officially moved to SI. Only the U.S., which uses the U.S. Customary System, Liberia and Burma have not officially adopted the SI standard.
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