A conversion factor can be more accurately described as a UNIT. A unit is something equivalent to 1. When we multiply something by 1, it doesn't change it's value, although it might change how it looks.
Example:
1 foot = 12 inches
Dividing both sides by 12 inches gives us this unit,
[tex]\rm \frac{1foot}{12inches}=1[/tex]
So when we multiply a quantity by (1foot)/(12inches),
we're really just multiplying that quantity by 1,
which doesn't change its value.