A. Greek Prefixes of the Metric System:
When you convert from feet to inches in our English system, you use a factor of twelve, i.e., 1 ft = 12 in. When you convert from yards to feet or from miles to feet you use other factors, three and 5,280, respectively. This problem of using a variety of factors is compounded when you consider that conversions are also made for volume and mass units. All these factors had to be memorized when you were going through your early years of schooling.

When the French academics developed the Metric System in the early 1790s, they chose a simpler method of creating different units of length. They chose a basic unit of length, mass, and volume, and then created larger and smaller units by adding Greek prefixes that indicated certain multiples, i.e., powers of ten.

You are probably aware of many of these from ordinary usage. For example, kilowatts of electrical energy on your electric bill, megabytes of storage capacity of a floppy diskette, or gigabytes of storage capacity on a computer hard drive.

Let us look at the common prefixes.

	Prefix		Symbol	Multiple
Large Prefixes	giga		G	109
	mega		M	106
	kilo		k	103
	deka		da	101
	THE BASIC UNIT			100
Small Prefixes	deci		d	10-1
	centi		c	10-2
	milli		m	10-3
	micro			10-6
	nano		n	10-9
	pico		p	10-12

B. Length:
The basic unit of metric length is the meter (m). This length is just a little longer than a yard. Let´s create larger and smaller units of length by attaching Greek prefixes that will indicate a multiple by a power of ten. By attaching the term kilo, we obtain kilometer, which is defined as 10³ meters. The two lengths would then be related as follows: 1 km = 10³ m.

If we attach the term centi, we obtain centimeter, which is defined as 10^-2 meter (a hundredth of a meter). The two lengths would then be related as follows: 1 m = 10² cm. Notice that since a centimeter is a hundredth of a meter, there must be 100 of them in a meter. By using this relationship, we can avoid the use of negative exponents in calculations where we wish to change from one unit to a different one.

Here is a list of the more common units of length, along with abbreviations, definitions, and relationships.

	Units of Length
Unit	Abbreviation	Definition	Relationship to the Basic Unit
kilometer	km	103 m	1 km = 103 m
meter	m
decimeter	dm	10-1 m	1m = 101 dm
centimeter	cm	10-2 m	1m = 102 cm
millimeter	mm	10-3 m	1m = 103 mm
micrometer	m	10-6 m	1m = 106 m
nanometer	nm	10-9 m	1m = 109 nm
picometer	pm	10-12 m	1m = 1012 pm

C. Volume:
The basic unit of metric volume is the liter (L). This volume is just a little bit larger than a quart. In the preceding section we created larger and smaller units of length by adding Greek prefixes to the meter. We can use the liter to create larger and smaller units of volume by the use of the same Greek prefixes. Here is a list of the more common units of volume.

Units of Volume
Unit	Abbreviation	Definition	Relationship to the Basic Unit
liter	L
deciliter	dL	10-1 L	1 L = 101 dL
milliliter	mL	10-3 L	1 L = 103 mL
microliter	L	10-6 L	1 L = 106 L

Another frequently used unit of volume is based on a cube that is 1 cm on each of its sides. This cube has a volume of 1 cubic centimeter (cm³ or cc). For all practical purposes, this volume is the same as a milliliter, and the two may be used interchangeably.

1 cm³ = 1 mL

Thus, 18.9 cm³ would also be 18.9 mL.

D. Mass:
The basic unit of mass is the gram (g). This is a fairly small unit of mass. For example, a penny has a mass of about 2.5 grams. Mass and weight are terms that are frequently confused with each other. Mass is an object´s resistance to change in motion. A stationary train takes a long time to begin moving due to its great mass. A motorcycle on the other hand, starts very quickly due to its much smaller mass. Weight, on the other hand, is a measure of gravitational attraction for a mass. On earth a person might weigh 150 pounds. On the moon, that same person would weigh only 25 pounds, since the moon has a gravitational attraction that is only 1/6th that of the earth. Since all of our measurements are made on earth, we shall use the terms interchangeably. Here are some of the more common units of mass.

Units of Mass
Unit	Abbreviation	Definition	Relationship to the Basic Unit
kilogram	kg	103g	1 kg = 103 g
gram	g
milligram	mg	10-3 g	1 g = 103 mg
microgram	g	10-6 g	1 g = 106 g