Measurement Systems

The International System of Units

Measurements are a very important part of any science course you will take. In fact, they are an important part of your everyday life. Imagine going to the gas station and asking the attendant for “three.” Three gallons? Three dollars worth of gas? Three WHAT? Measurements represent quantity, called a magnitude; however, they also have a unit. Their measurement and the unit chosen is dependent on the quantity being measured. Scientists around the world use the International System of Units, also known as the SI system. There are many advantages to using the SI system:

• In the SI system there is only one unit for each type of quantity. For instance, if you are measuring the mass of an object, you would always use grams.
• There are very few units in the SI system to worry about: only about 30. In the non-SI system there are thousands of different units.
• In the SI system, fractions or multiples of units are represented by simple, easy to pronounce prefixes like milli-, kilo- or giga-.
• SI units do not use fractions, they only use decimals. Consider this: have you ever tried to make a third of a recipe of cookies and you need to determine what 1/3 of 2/3 cup of sugar is?
• The SI system is based on units of ten. When making conversions between units, the decimal place just needs to be moved.

Basic SI Units of Measurement

You may be used to measuring length in inches, feet, and miles, but how does measuring length change in the International System of Units (SI)? Each type of measurement has its own unit in the SI system. In this interactivity, click on each of the spinning icons to learn more about the most important units of measurement you will use in chemistry.

Download a printable version of the interactivity.

 

Unit Prefixes

Prefixes are added to the base units to represent a larger or smaller quantity. The table below shows the major prefixes used in the SI system. Based on the prefixes, a millimeter would represent 1/1000th of a meter, while a kilometer would equal one thousand meters. The metric system may seem confusing at first, but it is actually very easy to use because it is based on the number ten. For example, there are ten millimeters in one centimeter, one hundred centimeters in one meter, and one thousand meters in one kilometer.

Prefix	Symbol	Meaning	Examples
kilo-	k	1000 times the base unit	0.001 kilometer 0.001 kiloliter 0.001 kilogram
hecto-	h	100 times the base unit	0.01 hectometer 0.01 hectoliter 0.01 hectogram
deka-	da	10 times the base unit	0.1 dekameter 0.1 dekaliter 0.1 dekagram
meter liter gram	m l g	the base unit	1 meter 1 liter 1 gram
deci-	d	1/10 of the base unit	10 decimeters 10 deciliters 10 decigrams
centi-	c	1/100 of the base unit	100 centimetes 100 centiliters 100 centigrams
milli-	m	1/1000 of the base unit	1000 millimeters 1000 milliliters 1000 milligrams

The SI system may seem confusing at first, but it is actually very easy to use because it is based on the number 10.  For example, there are 10 millimeters in 1 centimeter, 100 centimeters in 1 meter, and 1000 meters in 1 kilometer.  Are you still not so sure? Converting numbers between units only involves moving the decimal place.  Look at the chart above. The smallest unit has the prefix milli- and the largest unit prefix is kilo-.  To convert between units, you simply need to move the decimal point.  If you are converting to a smaller unit of measurement, move the decimal to the right one space for each prefix.  If you are converting to a larger unit of measurement, move the decimal to the left one space for each prefix.

SI Units Conversion Review

Practice your ability to convert measurements using the SI system in this non-graded activity. Read the directions associated with each question and provide the correct answer or answers. Then, click SUBMIT to check your response. Click the interactivity thumbnail and then click NEXT to get started.

 

Accuracy and Precision in Measurement

Now that you have explored the SI system of measurement, examine how to correctly record measurements. View this presentation to explore precision and accuracy in measurement using certain and uncertain digits, as well as how to determine the average or mean of a set of measurements.

View a printable version of the interactivity.