The metric system is a much more logical and straightforward system than the
old english system still used in the United States. Every other nation in the world uses
the metric system, so in today's global economy, it is very advantageous to learn
how to use the system. It is also the system used in science.
The metric system is based on the number 10, for example there are 10 millimeters
in one centimeter, 1000 grams in one kilogram, 100 centimeters in one meter, 100
degrees between the freezing and boiling point of water, etc.
Contrast this with the english system that has 12 inches to 1 foot, 16 ounces to
1 pound, 5,280 feet to one mile, 180 degrees Fahrenheit between the freezing and
boiling point of water, ... egad! All of the units in the metric system use a
common set of prefixes:
prefix  meaning  example 
pico  10^{12} = 1/10^{12}  1 picosecond = 10^{12} second 
nano  10^{9} = 1/10^{9}  1 nanometer = 10^{9} meter 
micro  10^{6} = 1/10^{6}  1 microgram = 10^{6} gram 
milli  10^{3} = 1/1000  1 millikelvin = 10^{3} kelvin 
centi  10^{2} = 1/100  1 centimeter = 1/100th meter 
kilo  1000  1 kilogram = 1000 grams 
mega  10^{6}  1 megasecond = 10^{6} seconds 
giga  10^{9}  1 gigakelvin = 10^{9} kelvins 
tera  10^{12}  1 terameter = 10^{12} meters

The base unit of length in the metric system is the meter. It is a little over
1 yard long, more precisely 39.37 inches long. Here are some other conversions:
1 meter (m)  = 39.37 inches  = 1.094 yards (about one big step) 
1 kilometer (km)  = 1000 meters  0.62137 mile 
1 centimeter (cm)  = 1/100th meter  0.3937 inch (1/2.54 inch, about width of pinky)) 
The base unit of mass is the gram. Mass is the amount of material in something
and is different than weight. See the
gravity chapter
for an explanation of
mass, weight and the difference between the two. There are 28.3495 grams in one
ounce. A paperclip has a mass of roughly one gram. Here are some other conversions:
1 gram (g)  = 0.0353 ounce  produces 0.0022046 pounds of weight on the Earth 
1 kilogram (kg)  = 1000 grams  produces 2.205 pounds of weight on the Earth 
1 metric ton  = 1000 kilograms  produces 2,205 pounds of weight on the Earth 
The base unit of temperature is the kelvin, though the Celsius is also used. The
kelvin scale is measured from absolute zerothe temperature at which all motion
stops, the absolute coldest temperature possible. The Celsius scale is measured
from the freezing point of pure water at sea level, but the intervals of temperature
are the same as the kelvin scale. Water freezes at 0° Celsius which is the
same as 273 kelvin. Water boils at 100° Celsius which is the same as 373 kelvin.
The Fahrenheit scale in common usage in the United States has the freezing point
of pure water at 32° Fahrenheit and the boiling point at 212° Fahrenheit
at sea level. Below are conversion formulae for Fahrenheit to the metric
scales and vice versa. Remember to calculate the values in parentheses first!
To convert Fahrenheit to Celsius use: ° C = (5/9)(° F  32).
To convert Fahrenheit to kelvin use: K = (5/9)(° F  32) + 273.
To convert Celsius to Fahrenheit use: ° F = (9/5)° C + 32.
To convert kelvin to Fahrenheit use: ° F = (9/5)(K  273) + 32.
See the light chapter
for further discussion of the kelvin, Celsius, and Fahrenheit scales.
Go back to previous section
last updated:
June 7, 2019
Is this page a copy of Strobel's
Astronomy Notes?
Author of original content:
Nick Strobel