Measuring amp power.


Is there a way to measure the wattage from an amp or integrated? I'm particularly interested in tube amps. 
adeep42
To all the responders, Thanks for your input. I don't think it was a stupid question, but some might (and obviously) disagree. 
 I actually love my amp in my current set up and have no intentions of upgrading. Merely a case of curiosity.
Btw, the amp is a Cary CAD 300-SEI. Over time I rolled the 6SN7s with NOS tubes from Brent Jesse. Replaced the 300Bs with AudioNote ones. It sounds entirely different than with the new Russian tubes originally provided.
The reason for my curiosity is that Cary specs the amp at 15 WPC. Most of the other 300B amps I see are spaced at 8-9 WPC including the Elekit TU-8600 I run in my second system.
My main system with the Cary has 97Db efficiency speakers. Even at relatively loud levels , the system is never challenged nor have I ever been aware of any clipping.
Thanks again to all. Please stay safe,

A