Rule to Remember -

If you are changing from a large unit to a smaller one (Example: feet to inch) you should multiply.
If you are changing from a small unit to a larger one (Example: inch to feet) you should divide.

big > small     =   multiply

Examples:

yards > feet
miles > yards
tons > pounds
gallons > quarts

small > big       =   divide      

 Examples:

feet > yards
yards > miles
pounds > tons