check amp watts

although, using ohms you might be able to figure it out with one of these 3 equations

I x E   

Isquared x R

Esquared / R

There are a lot of factors that determine the amount of power an amp is putting out at a given time. There are expensive testing equipment that can test max, or RMS output of an amp. But remember you may own a 1000watt amp and it during it entire life not produce 1000watts. This could go on for ever so here is a good rule to go by.

Add all fuses in the side of the amp togather. Multiply this number by 12.5 we all know when you jamin your system voltage is not 14.5 so dont use it. This number would be the amps max output if it were 100% efficient. Sorry its not so divide that by 50%. This is also considering other factors. This is close to the amps RMS power (useable power).

What you would measure would be voltage output.  If you set up your system and set head unit output and gains correctly using sine wave test tones recorded at 0 db....and are confident that the output is 100% clean (no clipping).....you can remove the speaker wires from the amplifer to test.  Probe the meter leads onto the amp's speaker outputs while the system is at full level and while playing the test tone(s) you used when you set it up.  The meter should be set to AC volts.  You'll get a continuous reading of voltage on each set of terminals that you had loads attached to.

You have to then use Ohm's Law to figure out power (watts).  Use a formula for finding power...in this case you know these two things:  the impedance load that you have attached to the set of terminals, and the voltage that you have just measured.  Look at the possible formula combinations HERE.  You would choose P = E^2 / R (because of your two known factors) .  Square the voltage reading (E times E) and divide that number by the impedance load (R) attached to that set of terminals.  Do the math and you will find the watts.