Marketcap as a whole is a pretty misleading metric. If everything sold suddenly, whether it is BTC or any stock, it wouldn't be for this total amount, each unit being sold lowper than the previous one. 

An aggregate of the transactions prices for each unit would make a lot more sense.

I know it exists for BTC, I don't remember how it's called. But I doubt there's such a thing for stocks though... 

 Fair point. 

 realized cap is the number you're thinking of 

and it's easy to calculate for Bitcoin but hard to calculate for silver and all these other things 

because they don't have a blockchain where all the transactions are visible