The metric system provides a logical way to organize numbers and mathematical thinking. The system is organized by giving names to each order of magnitude; that is, every time zeros are added to the place value (ones, tens, hundreds, thousands, etc.), metric system prefixes are used to indicate the value.
This is most commonly understood with units of measurement such as the meter. The meter is the basic unit of length and has no prefix. It therefore corresponds to the "ones" place in numerical value.
Prefixes are added as place values are added. For example, 10 meters adds a "tens" place to the number, which changes the name to a decameter (though this unit of measurement is rarely used). Next, 100 meters adds a "hundreds" place to the number, which changes the name to a hectometer. Add another zero to make 1000 meters, and you get a kilometer, a very common unit of length.
To recap:
1 meter = 1 meter
10 meters = 1 decameter
100 meters = 1 hectometer
1000 meters = 1 kilometer
As you can see, the metric prefix changes with each order of magnitude increase. This provides a simple way to understand exactly what each unit of measurement stands for in the metric system, since the prefixes tell you how much bigger a unit is than the base unit. This is different from the common system, in which inches, feet and yards aren't clearly related by size or by any linguistic connection.
The examples above show how prefixes indicate increasingly large units of measurement, but metric prefixes also create units smaller than the original by dividing it into fractions. A decimeter, for example is one-tenth of a meter, while the common centimeter is one-hundredth of a meter. This is most easily understood by considering how the decimal places keep adding a zero to hold place value as numbers get exponentially smaller:
1 meter = 1 meter
.1 meter = 1 decimeter
.01 meter = 1 centimeter
.001 meter = 1 millimeter
Not all metric systems prefixes are in common usage, though they are used regularly in scientific fields. You should also note that not all prefixes are used for every type of measurement.
For example, kilo- is used for both kilograms and kilometers, but centi- is only used in centimeters. One "centigram" might be easily understood to be .01 grams, but the word is skipped over in favor of saying "10 milligrams."
Below is a table of the most commonly used metric prefixes that can be added to the basic units of measurement, such as meter (length), gram (mass), second (time), and liter (volume):
Metric Prefix | Place Value | English Meaning | Usage Examples |
tera- | 1,000,000,000,000 | trillion | terabyte |
giga- | 1,000,000,000 | billion | gigabyte, gigawatt |
mega- | 1,000,000 | million | megaton, megawatt |
kilo- | 1,000 | thousand | kilometer, kilogram |
hecta- | 100 | hundred | hectare |
deca- | 10 | ten | decagon |
1 | one | [no prefix on the basic unit] | |
deci- | .1 | tenth | decibel |
centi- | .01 | hundredth | centimeter |
milli- | .001 | thousandth | milliliter, milligram |
micro- | .0001 | millionth | micron, microsecond |
nano- | .00001 | billionth | nanosecond, nanobot |
pico- | .000001 | trillionth | picometer |
A few metric prefixes have become common in areas of language not related to measurement. For example, mega- is often added to any word colloquially to show that something is very large:
The Mega-millions jackpot is huge this weekend.
The mega-monster is sure to be featured in the movie's sequel.
Likewise, micro- has become common to indicate that something is very small:
That micro-apartment in Manhattan still costs more than I can afford.
There's a fancy new microbrewery opening down the street.
It's worth the effort to memorize these common metric system prefixes so that you understand basic units of measurement and how they are related, even if you don't use the metric system on a regular basis. Understanding these numerical prefixes will help you get a ballpark idea of the size of an item when you read or hear the words in use.
Once you're familiar with the metric system you can learn the abbreviations for these units of measurement in our Measurement Abbreviations article.
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