Maybe this question is not related at all with Blender but, how i can define the real amount of roughness of a material? i mean, i know that by twitching and guessing with the less/more roughness bar will do the thing, but is there an official amount of roughness for each existing material? This question came to me because there are web pages that provide official IOR amounts for lots of materials of the real world, so i was wondering if there are web pages that provide the same information but of roughness of each existing material. I went to the internet and found nothing (maybe i'm just bad exploring internet), so... there's something like an official amount of roughness for each material IRL?
IoR can be categorized for transparent substances because it can be measured on the pure a state of the substance, letting the light through in an homogeneous, consistent measurable way.
Roughness - "the quality or state of having an uneven or irregular surface" - is hardly a scientific measure! Though in rendering terms it probably means something like "the probability of an incoming light ray to get randomly dispersed" (I'll let the experts correct or debate that one).
In reality (as opposed to computer generated virtuality), it is the result of the topology and complexity of the surface of a material at the macro and micro levels, most times also the result of presence of dust or other materials present on the surface. That mean the same substance can be rough or not based on how polished, clean, pure or unpure it is. Basically it is not really measurable or categorizable for specific type of substances like glass, ice, quartz etc...
If you find any "web page" doing this, I'd highly scrutinize the methodology before trusting it!