According to analysts at cryptocurrency company Chainalysis, of the existing 18.5 million BTC, about 20% lie in lost or otherwise blocked wallets. In total, this is about $140 billion.
Is this amount reported to anywhere or people are speculation only? I guess there are a lot of early bitcoiners have lost their BTC in such a proceed; either forget the encrypted password or have spoiled their drive, hardware etc. There was another article where I have read it was 1 million.
Since there is now way to be sure of that information unless people reported those coins themselves then it is obvious it is an estimation more than anything, however think about it if the number is close to being true and we add the coins of satoshi and the coins that institutional investors have bought then we realize that the amount of bitcoins actually floating around exchanges is very small and it is bound to get smaller as time passes and bitcoin becomes more popular. Also it is such a shame that this person cannot access his coins, most likely he never thought those coins will be worth much and now he cannot get access to his rightful fortune.