For PWM controllers, you get your "expected amps" from the array and then multiply the amps by 1.25 and get the nearest sized controller to that, going higher if practical.
What is my "expected amps"? Take the rated Isc (do NOT use the lower Imp figure!) off the panel labels and add them up if in parallel. You will get Isc in full sun at times and even more sometimes so that is what the 1.25 allows for.
EG, you have two 130w panels with Isc of 8.2a each in parallel, so your "expected amps" is 16.4a times 1.25 = 20.5a So in this case you could get a 20a controller. If the answer came to say 23a IMO get a 25 or 30a to stay above the margin of 1.25 times. (US NEC guide for that 1.25)
If you have MPPT, then your controller likely will clip the amps at its rating so you can ignore the 1.25 part. Also the new Bogart PWM has an amp limiter ISTR, but that is an exception for PWMs AFAIK.
