Hello Lawrence, the way to determine the amperage of the controller needed is quick and simple. you will need to know the total current output of your solar panel installation and you go with a solar charge controller with a higher amp rating. Fro example, if the total current (max) output of your solar panel installation is 48A, then you choose a 60A solar charge controller for the job.
 
If this is  not clear, I will be willing to provide further answer.