The metric system is a system of measures based
on powers of ten. The following are the fundamental units for the metric
system:
 meter, for length, abbreviated m
 kilogram, for weight, abbreviated kg
 liter, for volume, abbreviated L
Most countries in the world use the metric system
because of its following features:
1. The fundamental unit, such as the meter, can
be accurately reproduced without referring to a standard prototype. (A meter is
defined to be 1,650,763.73 wavelengths of orangered light in the spectrum of
the element krypton 86 and can be reproduced in a laboratory
anywhere.)
2. Units of the same type (i.e., length, weight,
or volume) are related by simple decimal ratios. (For example, a centimeter is
100 times smaller than a meter, so 2.5 m = 250 cm.)
The following diagram is useful for converting
units of length. Please note that each symbol is an abbreviation for length;
notice the fundamental length, meter (m), is in the center. The units to the
left are smaller than the units to the right. So a mm is smaller than a dm which
is smaller than a km. To convert from, say, a decimeter (dm) to a hectometer
(hm), count the number of spaces in between the units. Then, you only need to move the decimal to the left 3 times because you are changing from a smaller unit to a
larger unit (we would move the decimal to the right if we were changing from a larger unit to a smaller unit). For example, 5000 dm is a length
equal to 5 hm. If you had 100 km, how many cm would you
have?
3. Different types of units for length, weight,
and volume are defined in terms of each other. (For example, a liter is defined
with reference to the meter: it is the volume of a cube that measures 10 cm (or
1 dm) on each edge. Thus, a liter can also be called a cubic
decimeter.)
