Systems of Measurement

a ruler graduated in millimeters

Why do we need a measurement system? When experiments are performed there are almost always some observations where questions like "how fast", "how far", or "how much" must be answered. The only way to answer these questions is through measuring. Because of this, numbers in science will always have "units". These units are just as important as the numbers when communicating observations. Never write a number without its units.

A "standard" is something that is used as a comparison for measuring. Two things are important for any standard:

The English System of Measurement is commonly used as the day to day system in the United States. Since we are familiar with this system, we know about pounds, feet, and gallons. But what are the standards for these units? Because there are no standards in nature for these units, the rest of the world has moved to another measurement system.

It might be alright to use the English System when communicating with others in the United States, but what about communicating with the rest of the world? Scientific discoveries are made all over the world. It is important that observations made in one country can be verified by someone in another country. For this reason, science observations must be measured using standards that are available around the world.

The International System of Measurement - SI, is commonly called the Metric System in the United States. Each of the units within this system has an unchanging standard found in nature all over the earth. This is the system used in all science measurements.

what are the standards?


Prefix        		decimal equivalent     	exponential equivalent

 Pico            		0.000000000001            10-12

 Nano              	0.000000001             	10-9

 Micro             	0.000001                	10-6         (Most commonly used with a microscope)

 Milli             	0.001                   	10-3

 Centi             	0.01                    	10-2

 Deci              	0.1                     	10-1

 no prefix         	1.0                     	100

 Deka             	10.0                     	101

 Hecto           	100.0                     	102

 Kilo           		1000.0                     	103

 Mega     		 1,000,000.                      106

 Giga  		1,000,000,000.               109



Some of the common SI unit relationships used in science classes:

Refer to these guidelines for correct use link to an Internet Website to avoid common mistakes when using the International System of Units.

Using the Metric System is difficult only because:

Unit Conversions:

Having to convert one type of unit to another is a common problem in science. There are exact conversion factors that can be used to change units in one system to units in the other. Here is a page of useful conversion factors. We will not stress conversion between the systems in this class. All our measurements will be done using SI units. The table below might help you begin to visualize the size of the units of the metric system.

An approximate comparison of the two systems:

English SystemMetric System
1 yard0.9 meter
1 mile1.5 kilometer
1 pound0.5 kilogram
1 quart
4 quarts = 3.8 liters
~1 liter

Research Links:

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