This document discusses the International System of Units (SI), which is the standard system of measurement used internationally, especially in science. It notes that SI provides a coherent and rationalized system of measurements based around powers of ten. Key aspects of SI include standardized prefixes that indicate multiplicative factors of units and a unified system of measuring length, mass and volume. SI aims to make scientific measurements easily understood worldwide.

1. Measurement
The
International
System of Units

2. Why do we need to be able to
measure things?
Suppose we wanted to
measure a 2 x 4 for
building a house.
Numbers by themselves don’t
make sense.
To make sense, all measurements
need both . . .
Units by themselves don’t
A Number and a Unit!
AA bbooaarrdd iiss 3m5e0t elorsn g l o. n. g. .. . . .
Any Ideas?

3. Precision and Accuracy
Precision is a
description of how
close measurements
are to each other.
Accuracy is comparing
your measurement to
the actual or accepted
value.

4. Why use SI?
In the U.S. the English
System Scientists is used. use the Most SI
of the
rest worldwide of the world because:
use the
Metric or SI.
 Measurements are easily understood by all scientists
 Measurements are easier to convert than the English
system
The SI (International System of Units) is the form
of measurement typically used by scientists.

5. In the English system you have to
remember so many numbers . . .
 12 inches in a foot
 3 feet in a yard
 5,280 feet in a mile
 16 ounces in a pound
 4 quarts to a gallon

6. In the SI you only have to remember one
number.
The SI is based on the number 10.

7. The SI System uses the following prefixes:
POWER PREFIX SYMBOL POWER PREFIX SYMBOL
+ 30 dea D -1 deci d
24 yotta Y -2 centi c
21 zetta Z -3 milli m
18 exa E -6 micro 
15 peta P -9 nano n
12 tera T -12 pico p
9 giga G -15 femto f
6 mega M -18 atto a
3 kilo k -21 zepto z
2 hecto h -24 yocto y
1 deka da -30 tredo t

8. This system works with any SI measurement.
The UNIT becomes whichever type of
measurement you are making (e.g., mass,
volume, or length).
It is the same system regardless if you are
measuring length, mass, or volume.

9. It works for all types of measurement.
If you’re measuring . . .
MASS, it is the gram
(centigram, milligram,
etc.)
VOLUME, it is the
liter (deciliter,
hectoliter, etc.)
LENGTH, it is the
meter (kilometer,
decameter, etc.)
centi gram
The first part of the term indicates the amount, the
second part indicates the unit of measurement.

10. Thus . . .
2,321.0 millimeters to meters
521.0 grams to hectograms
8.5 kiloliters to centiliters
= 2.321 meters
= 5.21 hectograms
= 8,500,000 centiliters
NOTE: The digits aren’t changing, the
position of the decimal does. In
the English system the entire
number changes.

11. So why SI?
Because SI is:
 simple
 coherent
 rationalized

12. How do we write in SI?
An SI unit symbol is:
 written in print.
 always written in singular form.
 not capitalized unless derived from a proper
name.
 not followed by a period.
 not abbreviated.