I have a lot to learn before that would be useful.
Getting around a scope isn't terribly 'thick' for what you want to do, from what I understand.
They can be hard to ballpark. SS amps which require a certain ohmage load might sound much less loud than a tube amp of <1/5th the wattage rating IME, even when at min-ohm loads, that's no way to tell 'how loud' even.
Brands tend to be 'linear' in amp naming, a '10' amp will be smaller than a '40' and 40 smaller than 100.
There was much talk of English and American watts back when ['70's], around here, but that faded out.
I just go by the # of and type of tubes to get a ballpark idea.
Most of the SS amp ratings seem to be somewhat congruous with one amp to the other, the 'min-ohmage' deal can make a big difference in how much you can actually get out of any particular amp though.
It's an 'average' thing to discuss for the most part, frequency, picking strength attack and many other things can cause the output to rise and fall...very far.
It becomes fairly immediately evident [such as experiencing being drowned out, or not being able to get clean sound], and a signifigant increase in available watts is the solution.
Which is no help at all for explaining how to measure watts...