According to the following source, GRIN's marketcap is $4B (making it a top 5 coin by marketcap):
https://messari.io/asset/grinSorry guys, the favorite shitcoin of bitcoiners is definitely overvalued! Trade all your GRIN back to bitcoin!
Current price is ~$4. Current supply is 709,000 coins. So current market cap is now is $2.8 million. Which puts it into the 500s rank on CMC.
Of course it is inflating rapidly with 72,000 coins issued per day. So if it can hold its current price of $4, by the end of 12 months it would have a market cap of ~$124 million. Which would put it slightly ahead of Bitcoin Diamond in rank 40...
My preferred metric is to look at the 3 year supply which values it between Maker and ETC. Which is a top 20 slot. But that 3 year time line also puts us deep into the next bullmarket so who knows.
So I dont know where $4B valuation comes from, unless you intend to wait 30 years at the current price.
One of the Twitter guys with a quite notable number of followers had tweeted a very good explanation for that $4B number. However, I've spent my 30 minutes searching for his tweet and totally unable to find it. It seems like he deleted it (this makes me believe a little that the explanation was not accurate).