How much power do I need? Find out using this method...

I've been hanging out on diyaudio and ran across this simple technique to measure the power used by your speakers.  So many discussions here revolve around this question that I thought I'd post the method...

If you have a multi meter, you can use the test tone & technique provided here to calculate how many watts your speakers actually use:

It’s super informative & useful: all you do is set your volume at the max listening level you use, then play the -12db 120hz test tone while measuring voltage at the speaker terminals. Square that value and you’ve got the maximum watts needed. Plenty to read at the link...
A peak level 10 db above average requires 10 x the power in watts, approximately.
For a speaker rated at 90db:
1 watt should produce 90db
2 watts 93 db
4 watts 96 db
8 watts 99 db and so on...
Keep doubling the power to gain 3db.
Every 10 db should double the "perceived" volume.
roberjerman, your ears are shutting down because of distortion not volume. I routinely subject innocents to 95 dB after appropriate warm up.
They start trying to talk to you not realizing how loud it is. Now most rock concerts are up at 110 dB but that volume is unnecessary to get the feeling you are there without damaging your ears. 95 dB is perfect. But, very few systems can do that effortlessly.
gs5556, I can easily hear one dB. 3 dB is painfully obvious and 6 dB is an earthquake. You need to live with a system that accurately measures volume in dB or a dB meter. Volume at distance is more complicated because you are listening to a stereo pair. As you move closer to one speaker you move away from the other. Volume one meter out from one speaker is almost the same at the listening position. Just use the meter at the listening position. That is where it counts. Measuring power of the speaker terminals with a high impedance meter is perfectly appropriate. It won't be a perfect number but close enough to give you an idea what is happening.   
I'm confused with the 6db being an earthquake?  Are you referring to 95 as the base line and +6db as the earthquake?  My system isn't so unusual but 95 db is a joke.  My Coincident speakers are 94db at 1 watt.  My 325 watt Mac is overkill to attain 95db.  My other amps are 100 watt tube monoblocks which obviously have different distortion than the Mac.
Would I call 95 loud?  Sure.  95 for a movie is more likely.  Dynamic headroom is a big difference.  No one listens at an exact sound pressure level the whole time.  I'm a bit confused.
Hi elevick. You have solved the problem by having very efficient loudspeakers and with your Mac you should have no problem making your ears bleed as long as the speakers can perform at those volume levels. Many if not most can't. But I have no experience with your speakers. The problem for most people running those levels is that either the amp is clipping transients or the speaker is distorting. 
I was responding to gs5556's comment about differences in perceived volume levels. To any listener a 1 dB increase in sound pressure is obvious, 3 dB is a rather large increase and 6 dB is a huge increase. If I were to increase the volume 6 dB on one speaker only the other one would literally disappear. Try it. There is another issue with point source speakers. They way the cast an image makes them sound surreal at loud volumes. It is like having the volume of the 6th row back in the 20th row.
Line source or linear arrays solve this problem by casting a much larger image so the volume and the row match up. 
In no way do I listen to all music at 95 dB. Also remember that the rating of your speaker is at 1 meter. I listen at the volume the music at hand sound right. There is a rare record that I will listen to at 100 dB like the Dead's Infra Red Roses. What fun to blow peoples brains with that one. If you want to know how your system and house deal with very low frequency transients get that disc. It is a selection of drum solos. Every recording has a "right" volume level depending on the type of music and the way it was mastered. I miss spoke. Some recordings have no right volume level usually because they are mastered poorly. As an example I was listening to Paul Simon's Graceland last night. The instruments are way out in front of his voice like he is standing in the next room over. So either the band is too loud or his voice is too far away. I love the music but it could have been mastered better or at least more realistically. Most people think this is a great recording. Waiting For Columbus is an excellent job all around. Turn it up and the band is right there everything in perspective. It was probably mastered off the sound board. For studio recordings check out The Smiths, The Queen is Dead. Great job! Waltz for Debbie I listen to at 90 dB. These are peaks by the way, peak volume measured with a dB meter. My preamp measures volume in dB but that has nothing to do with absolute sound pressure levels. dB is a relative term.