Normally you could read the specs on your speakers, or check their website for technical specifications or consumer help.
Electronic techs use expensive test equipment, like a True RMS AC Power Line Analyzer, for accurate measurements.
You could try hooking a voltmeter to your speaker leads when you play your amplifier.
Using the formula, (V^2)/R voltage times voltage divided by impedance. Be careful you don't explode each satellite & blow a hole in the floor!
Wattage, the power a system draws, can be measured three ways:
* RMS (Root-Mean Squared)
* RMS Maximum - The maximum power a system can reliably handle in bursts.
* PMPO - the maximum output, Peak Maximum Power Output
