The SI SystemEdit

The International System of Units (SI) comes from the French Systeme International d’Unites, which was established in Paris through the Treaty of the Meter on May 20, 1875. At the time, 48 nations (including the United States) signed up to this treaty. Since then, that number has risen to 51. The SI is maintained by the International Bureau of Weights and Measures (BIPM), and is updates every few years by the General Conference of Weights and Measures (CGPM). Their next meeting is scheduled for the year 2007. Why was this system created? Prior to the Metric System there was a lot of confusion between people in different areas because everyone had a different standard of measurement. The purpose of this system is to ensure worldwide unification of physical measurements. Presently, there is an economic necessity to adopt this system. There are 3 conditions for this system: 1. There is one fundamental unit for each quantity. 2. Multiples and fractions are created by adding prefixes to the originally defines units. 3. Fundamental units are defined rationally and are related to each other in a rational fashion.


Here are the definitions of different types of quantities:

Quantity in the General SenseEdit

A nonspecific property that is given to phenomenon, bodies or substances (ex. Mass, electric charge).

Quantity in the Particular SenseEdit

A quantifiable or assignable property which is given to a particular phenomenon, body, or substance (ex. The mass of the moon, the electric charge of a proton).

Physical QuantityEdit

A quantity that can be used in mathematical equations of science and/or technology.


A particular defined physical quantity with which other quantities of the same kind are compared to express their value.

Value of a Physical QuantityEdit

Expressed as a number and a unit. There are 7 base quantities in the SI system:

Base QuantitiesEdit

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The table's caption
Base Quantity Name Symbol
Length Meter m
Mass Kilogram kg
Time Second s
Electric Current Ampere A
Temperature Kelvin K
Amount of Substance Mole mol
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3 Kilo k

☺FUN FACT: The meter was originally defined as the distance between the equator and the North Pole. ☺There are also 22 derived units that can be formed using these established values. While these units are the accepted units in the SI system, there are other units that have been deemed compatible for use with the SI system. An example of some of these units would be the minute, the hour, and the day.


Prefixes in the SI System:

The table's caption
Exponent Name Symbol
24 Yotta Y
21 Zetta Z
18 Exa E
15 Peta P
12 Tera T
9 Giga G
6 Mega M
3 Kilo k
2 Hecto h
1 Deka da
-1 Deci d
-2 Centi c
-3 Milli m
-6 Micro µ
-9 Nano n
-12 Pico p
-15 Femto f
-18 Atto a
-21 Zepto z
-24 Yocto y

→Prefixes can be added to units to express that the unit is raised to that power of 10.

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