power or loudness of a PA System is measured in watts.
Speakers and amplifiers always show the wattage in the
spec (e.g. 300 watts) and the number of watts can be shown as Peak power or
RMS. Peak power is the maximum it's capable of, RMS
(which stands for 'route means square') reflects the average amount of power it can
comfortably and continually produce for a long period and is the rating you
should always go by. Always go with as much power as you can afford. You
shouldn't have your
PA system turned up to its full
capacity because any peaks may cause distortion, and your
speakers will have a longer life if they're not always running at their maximum.