Steps for Factor-Label method
The factor-label method is very useful to keep track of all your units and when you have to convert
several units in one problem.
1) Make sure you know the conversion factor you will use (ex. 1 mile = 1.609 km)
2) Write the number you want to convert and place it over 1
Ex. Convert 4.5 miles to kilometers
4.5 𝑚𝑖𝑙𝑒𝑠
1
3) Multiply the number by your conversion factor so that the unit you are getting rid of is opposite
of the starting #s unit. You want the units to cancel so they have to be diagonal from one
another. The number that is with those units in the conversion factor must stay with those units.
For example, in the conversion factor 1 mile = 1.609 km, you must keep the # 1.609 next to the
units kilometers.
4.5 𝑚𝑖𝑙𝑒𝑠
1.609 𝑘𝑚
×
=
1
1 𝑚𝑖𝑙𝑒
4) Continue to set up other conversion factors to the units you want to get rid of are always
diagonal from each other and cancel. Carry out the math on your calculator, and write your
answer with the correct units.
Ex: Convert 45 seconds to hours
45 𝑠𝑒𝑐
1 𝑚𝑖𝑛
1 ℎ𝑟
×
×
= 0.0125 ℎ𝑟𝑠
1
60 𝑠𝑒𝑐
60 𝑚𝑖𝑛
In this example, you would take 5, divide by 60, then take that answer and divide by 60.
All your units cancel except the hours so your answer will be in hours.
Note you can use the factor label method to convert a number with two units to two new units all in
one step. An example of this would be speed.
EX: What does 75 m/s equal in miles/hour? You need a few conversion factors: 1000 m=1 km, 1.609
km=1 mile. All the units cancel except the miles and hours. The seconds on the bottom, must cancel
diagonally with the 60 seconds later on.
75 𝑚
1 𝑘𝑚
1 𝑚𝑖𝑙𝑒
60 𝑠𝑒𝑐
60 𝑚𝑖𝑛
×
×
×
×
= 159.9 𝑚𝑖𝑙𝑒𝑠/ℎ𝑜𝑢𝑟
1 𝑠𝑒𝑐
1000 𝑚
1.609 𝑘𝑚
1 𝑚𝑖𝑛
1 ℎ𝑜𝑢𝑟
You can plug this into a calculator by putting: 75 ÷ 1000 ÷ 1.609 × 60 × 60