SI Units, Metric Conversions,
& Dimensional Analysis
Good Morning Boyzzzz…
1. How many seconds are in 9.7 hours?
2. How did you figure out that answer?
• A major theme of science
is communication and
collaboration. We need a
single measurement
system for everyone.
• Le Systeme International
d’Unites - SI
SI UNITS
Quantity
Unit Name
Abbreviation
Length
Meter
m
Mass
Kilogram
kg
Time
Second
s
Temperature
Kelvin
K
Amount of
substance
Mole
mol
Electric current
Ampere
A
Luminous intensity
Candela
cd
• We use SI prefixes to represent quantities
that are larger or smaller than the base
units.
Prefix
giga
mega
kilo
hecto
deca
Abbreviation
G
M
k
h
da
deci
centi
milli
micro
nano
d
c
m
μ
n
Conversion
1 Gm = 109 m
1 Mm = 106 m
1 km = 1000 m
1 hm = 100 m
1 dam = 10 m
1 meter (1 m)
1 m = 10 dm
1 m = 100 cm
1 m = 1000 mm
1 m = 106 μm
1 m = 109 nm
Dimensional Analysis
• Dimensional Analysis is a method used to
make conversions. This method helps us
organize information without becoming
confused about what units are being
cancelled or multiplied/divided.
Rules
1. You must use Dimensional Analysis to
solve conversion problems
2. Always show all your work
3. Include units
4. Make sure your units cancel out
5. Everything on the top is multiplied
Everything on bottom is divided from the top
Conversion Factors
• A ratio (or fraction) derived from the
equality between two different units that
can be used to convert from one unit to
the other.
• Conversion factors always equal one
because the two values are equal to each
other.
Conversion Factors
4 quarters
1 dollar
=1
=1
1 dollar
4 quarters
60 minutes
1 hour
=1
=1
1 hour
60 minutes
1m
100 cm
=1
100 cm
=1
1m
Convert 62.0 inches to centimeters
• First we need to map out what we are
doing.
62.0 in  ___ cm
Convert 62.0 inches to centimeters
• Second we need to determine our
conversion factor
How many centimeters are in one inch?
2.54 cm = 1 in
1 in
2.54 cm
=1
2.54 cm
1 in
=1
Note: We could have also
used that 1cm = .394 inch
but as a general rule, the
larger unit gets the 1!
Convert 62.0 inches to centimeters
• Third, we multiply our given by the
conversion factor…making sure to arrange
the conversion factor so that the units
CANCEL!
62.0 in X 2.54 cm
= 157.48 cm
1 in
Note: Units that are both on the top and the
bottom cancel
Convert 62.0 inches to centimeters
• Lastly, we make sure that we reached our
“destination” and that we have the correct
number of significant figures.
157.48 cm  157 cm
Note: Conversions factors do not follow
significant figure rules, they are not
measured and do not show accuracy.
Multiple Conversions
• When conversions require several steps,
Dimensional Analysis is extremely useful.
It helps organize information so we can
think through problems step-by-step.
How many feet are in 965 cm?
• 1. Map it out: 965 cm  ___ ft
• 2. Find conversion factors:
How many feet are in 965 cm?
965 cm
X
1 in
2.54 cm
X
1 ft
12 in
= 31.66  31.7 ft
You are cooking for a large group of
people. You must change the recipe to
accommodate all the guests. How many
gallons will 384 teaspoons of vanilla
extract occupy?
– 1 Tablespoon (T) = 3 teaspoons (t)
– 1 cup (c) = 16 Tablespoons
– 1 pint (pt) = 2 cups
– 1 quart (qt) = 2 pints
– 1 gallon (gal) = 4 quarts