Metric System

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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 = 1/1012 1 picosecond = 10-12 second
nano 10-9 = 1/109 1 nanometer = 10-9 meter
micro 10-6 = 1/106 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 106 1 megasecond = 106 seconds
giga 109 1 gigakelvin = 109 kelvins
tera 1012 1 terameter = 1012 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 zero---the 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.

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last updated: June 7, 2019

Is this page a copy of Strobel's Astronomy Notes?

Author of original content: Nick Strobel