YOu don't, it's how "real" amps are rated. If you for example to your amp and looked at it's ratings, you might notice that the power they "say" it does is not at full bandwith less then 1% distortion. To make a long story short, it will do the power it says it puts out only when lightning strikes it. Real amps don't rate peak power aka us amps......There is nothing wrong with decent amps that aren't 1000$ but don't think for one minute that a 500$ amps does anything near the power or a 1000$ amp. So if an Us Amps AX1000 is 1000 watts RMS and costs 999.99 how in the hell is a 500$ amp from another company 2000 watts RMS?????? It's simple, the ax1000 does what it says it does, the other does not. Don't get fooled.