A conversion factor is the number used to convert a measurement from one unit to another. For example, one hour is equal to $60$ minutes which means that the conversion factor from hours to minutes is $60.$ $$2\text{ hours}\cdot 60=120\text{ minutes}$$ The opposite conversion, from minutes to hours, has the conversion factor $\frac{1}{60}.$ Therefore, it is always important to know in which order to convert.