Ohms Law will let you calculate how much power your getting. But if you didnt know that then you probably dont have the tools or knowledge of how to measure/calculate. To easily set your amp gain for subs: Set low pass to 120Hz. Set gain on amp to minimum. set head unit to regular bass/treble/fade settings. then turn music up to 80% of full volume. Now adjust gain up until the output of speakers sound best (not distorted, not clipping, not popping). viola