The factor label method is used to convert units from one form to another by using conversion factors. It involves identifying the given and desired units, finding the appropriate conversion factor ratio, arranging the factors so that like units cancel out, and then multiplying the numerators and dividing by the denominators. Examples are provided to demonstrate converting between time, distance, and rate units like hours to seconds, miles to inches, and miles per hour to feet per second. Memorizing metric prefix conversions is also important for using this method between metric units.

1. FACTOR LABEL METHOD & CONVERSION
FACTORS

2. FACTOR LABEL METHOD
• A method of converting units from
one form to another.
• Must have a conversion factor
to perform factor label method
that is arranged so that like units
cancel.
• Significant figures still matter
• Our final answer will have the
same # of sig figs as the number
we are converting

3. CONVERSION FACTOR
• Used to convert a measured
quantity to a different unit of
measure without changing the
relative amount.
• It is a ratio (fraction) that equals
one
• Examples:
• 1 inch = 2.54 cm =>
1 inch/2.54cm
• Aka a bridge
• See first page in text for unit
conversion factors

4. EXAMPLE: LET’S START OFF EASY…
• Let’s say we want to find out how many centimeters are in 21.5 inches
1. Identify information wanted & information given
21.5 inches = ?? Centimeters
2. Identify unit conversion(s) to be used
2.54 cm = 1 inch
3. Arrange conversion factor as shown:
**only true if our desired units do not have a unit in the denominator**
Desired units
Original units
4. Multiply the numbers in the numerator, and the numbers in denominator
5. Divide the numerator by the denominator

5. FACTOR LABEL METHOD
• Converting 21.5 inches to centimeters:
• Conversion Factor: 2.54 cm
1.00 in.

6. EXAMPLE: LET’S MAKE THINGS A BIT
TRICKIER…
• Ex: how many hours are there in 7200 seconds?
1. Identify information wanted & information given
7200 sec. = ?? hours
2. Identify unit conversion(s) to be used
60 sec = 1 min
60 min = 1 hour
3. Arrange conversion factors as shown:
Desired units
Original units
4. Multiply so that units cancel

7. FACTOR LABEL METHOD
Ex: how many hours are there in 7200 seconds?
1. 7200 sec. = ?? hours
2. 60 sec = 1 min
60 min = 1 hour
3 & 4. 7200 sec. x 1 min x 1 hour = 2 hrs
60 sec 60 min

8. EXAMPLE: YOUR TURN!
Try this one: How many inches are in 1.00 miles?
1. Identify information wanted & information given
2. Identify unit conversion(s) to be used
1. Arrange conversion factor as shown:
Desired units
Original units
4. Multiply so that units cancel

9. EXAMPLE
How tall are you…
- In inches?
- In meters?
- In miles?

10. EXAMPLE: CONVERTING RATES
• What is 65 miles per hour converted to feet per second?
• NOTE: the word “per” identifies that there is a ratio
• Rewrite as 65 miles and feet
hour sec

11. EXAMPLE: THE MORE DIFFICULT STUFF!
What is 65 miles per hour converted to feet per second?
1. Identify information wanted & information given
1. Identify unit conversion(s) to be used
1. Arrange conversion factors so that desired units are left
2. Multiply so that units cancel

12. FACTOR LABEL METHOD
• This method can also be used to convert between metric unit prefixes
• Ex: how many meters are in 52 cm?
52 cm x 1.0 m = 0.52 m
100 cm
• You should memorize all metric conversions from kilo through milli
prefix mega kilo hecto Deka Deci Centi Milli micro
Meter
Gram
Value 106 103 102 101 Second 10-1 10-2 10-3 10-6
Liter
m
Abbrev- g
M k h da d c m μ (“mew”)
iation s