A typical car amplifier can be found in the range of 10-30 Amps. You can check the amount of power you need by looking at the fuse near the inputs.
What amp do I need for 4 speakers and a sub?
A four-channel amp works to power: Four speakers; Two speakers and a subwoofer—you can use a four-channel amp to power a subwoofer and two rear full-range speakers by bridging two of the channels to power the sub.