Metric System

In science metric units are used to quantify physical parameters.  Only Myanmar and Liberia join the non-scientific people of the United States of America in using other systems.

REVISE: The types of parameters one needs to describe include length, mass, force, time, temperature, work/energy, power.  In the international system (Le Système Internationale), or SI the base units for these quantities are meter (m), kilogram (kg), Newton (N), second (s), Joule (J), and Watt (W).  Some of these are derived (like Newton = kg*m/s2)

The metric system is based on decimals, or cutting things into tenths.  This means it is easy to move between units, as all one needs to learn are the prefixes telling you have far to move the decimal.  Prefixes placed in front of the base units indicate the factor by which it has been divided or multiplied.  This allows one to utilize quantitative measures that are not extremely large or small.  You can have 4 nanoseconds instead of 0.000000004 seconds.

Divisive Factors

When one is describing something smaller than the base unit, one must use a factor that will result in something smaller.  This means that the decimal point will be moved to the left.  For example, the factor “milli-” abbreviated “m” is used to indicate the factor 10^-3.    So if you have 1 milliliter that is the same as 1 mL, or  1 x 10^-3L, or 0.001 L.  5 mm is 5 x 10^-3 meters or 0.005 m.  Note, that with all factors that divide the unit into something smaller, you will end up with more of the small unit than there was of the original.   Think of dividing a dollar into dimes or pennies.  You end up with more of the smaller unit.  You could call a dime a decidollar, or a penny a centidollar.  This might help you decide if an answer is reasonable when you are converting liters to deciliters, or meters to centimeters.

Commonly used prefixes, their abbreviations, and factors to make the base unit smaller are:

deci-       d        10^-1

centi-      c          10^-2

milli-       m        10^-3

micro-     μ         10^-6

nano-       n         10^-9

pico-         p         10^-12

fempto-    f          10^-15

Note that μ is the Greek lower case letter mu and is pronounced like you are a happy bovine saying “moo”.

Multiplicative Factors

When one is describing something larger than the base unit, one must use a factor that will result in something larger.  This means that the decimal point will be moved to the right.  For example, the factor “kilo-” abbreviated “k” is used to indicate the factor 10³.   So if you have 1 kiloliter that is 1 x 10³ L or 1000 L.  5 km is 5 x 10³ meters or 5000 m.  Note, that with all factors that multiply the unit into something larger, you will end up with less of the large unit than there was of the original.   Think of exchanging one dollar bills for a 10 dollar or 100 dollar bill.  You end up with fewer of the larger unit.

Commonly used prefixes to make the base unit larger are:

kilo-        k       10³

mega-     M       10⁶

giga-       G         10⁹

tera-       T          10¹²

peta-      P          10¹⁵

Agricultural and Natural Resources Units of Measurement

Acres and hectares are units to describe land.

An acre is used in the United States.  It is is 1 chain by 1 furlong.   A chain is 66 feet long, and a furlong is 660 feet long.  An acre is   ¹⁄₆₄₀ of a square mile.  A mile is 5,280 feet or 1,760 yards.  The chain derives from the use of an actual chain with 100 links created in 1620 by a mathematician and clergyman named Edmund Gunter for use in surveying land.

A hectare is not an SI unit, but is recognized for use with the SI system to describe areas of land.  It is 10,000 m².  This is 100 m by 100 m, or ¹⁄10 of a square kilometer.