finding true wattage

I was wondering if there was any way to use a DMM to get a rough idea of the true wattage an amp is putting out.

For example if I have an amp that states it can put out 200rms @ 4 ohms, is there any way I can use a DMM to verify this?

So without acces to any equipment other than a DMM and not needing to be exact, 2 doors down on the left will do.

If I take the amp, ran a 100hz test tone to a known 4 ohm load. Could I take the V^2/4 and get in the general neighborhood.

All I am trying to figure out is if an amp I have is pushing 100 watts or 200 watts or somewhere in the middle.

Consider this, if you will, before putting all efforts into testing "to get in the general neighborhood":  most of what you listen to is powered with under 1 watt.  Outputs in the hundreds of watts are so brief, in real life, that you can rig up testing guesswork all day long and never find out true RMS output...which means it doesn't make a bit of difference whether the amplifier reaches 100 watts or pushes out that 3db higher at 200 watts if it is providing what you want it to.  If it's a good amp, you will know.  If it's junk, you will know.