How many watts??

VU Meters were all the rage in the 60’s and 70’s… McIntosh being one prominent adherent well into today. Big reason why they were dropped was because a lot of people noticed they were not using that much power to “swing the needles” 

So trying to sell a triple digit amp when people were armed with knowledge didn’t seem like the path capitalists wanted to take. Some manufacturers even build power hungry speakers just to sell their big watt amps… see above for example.

The total power of a amplifier should be taken with the knowledge that you should have enough headroom for dynamic passages. Lots of amps will run in pure class a for the first few watts. You also should take into account the load the speakers present. Inefficiencies will require power.  For example, you could run a pair of very efficient horn speakers, like Klipsch with a modest few watt tube amp and enjoy satisfying volume. 

The rule of thumb is: 10 times the average power in watts to avoid clipping. So with 80 watts you can use 8 watts average. That 8 watts into a 90 db sensitivity speaker will produce about 99 db continuously - if you can stand to listen that loud!

Matching the wattage to the speaker sensitivity is important! You wouldn't want to drive Magneplanars with a 3.5 watt SET tube amp!

Nor a Klipschorn with a 200 wpc amp!

If I have a 80 watt stereo amp and I normally listen at quarter volume and never play at levels higher than this. Do I really need 80 watts could I use a 15 watt amp at half volume?

My next question if I have speakers that my mfg states needs min 50 watts to really make them sound good with my current amp rated at 80 watts but played at qtr volume does that mean I am not really getting the best from these speakers. If I play at half volume this is too loud, do I need a bigger room. Sorry if I did not explain clearly enough.

An oscilloscope might tell you what the maximum voltage is you are presenting to the speakers. Once you know that, then you could make an objective decision.

Or just hook up your amp and subjectively determine if it sound good to you.