We know roughly how many btc have been mined,but anyone any rough idea or guess how many have been lost in cyber space or old wallets with a tiny amount in them abandoned never to see the light of day again.
If you include Satoshis coins a fair bit
But if you include actual coins lost there are the dumping addresses and then a few coins are destroyed now and then but I would say less than 1% of all coins mined at this stage in time
The mtgox coins are more less around but they could be considered lost as well.