I guess the question should be rephrased then as "how much have the current owners of bitcoin collectively exchanged for their coins?" This question also becomes more interesting when you factor in every coin that has been mined but not yet exchanged for money. I believe the GP is correct in guessing that the number will be much smaller than the current market cap of BTC
The number is without question much smaller than the current market cap of BTC. The current price and number of shares traded on the exchanges is not very meaningful since exchanges are unregulated and you have behavior such as wash trading where you can manipulate the price and inflate volume.
What I would like to know is how much money has actually been transferred into the exchanges. That is what matters. If Coinbase has 12 million accounts, and on average only $100 was invested (I'm assuming there are MANY opened yet unfunded accounts), then we're talking about $1.2billion at play moving back and forth on that exchange. (this is just a hypothetical number, I would love Coinbase to produce statistics, but know they have no incentive to.)
If no new accounts get opened and no more money flows in, That $1.2b will slowly drop to zero as Coinbase and the miners eat up that pool with fees.
You do put money into a company when you buy its shares ... during an IPO. Meanwhile, owning shares of a company convey fractional ownership of it, its assets, and its future earnings. People will consider the stock price of a company relative to its assets and earnings (P/E) as an indicator of whether the company is overpriced or under-priced.
No one really notes the "total volume" of the trades of stocks, which is what you're asking for for Bitcoin; it isn't really a meaningful number. If people pass a stock
- or a Bitcoin - back and forth for 10 trades for [$99, $101] or for 100 trades for [$99, $101], it isn't really meaningful.
The best you can do for Bitcoin is to try to gauge the "depth of the market" right now, ie, how many "buy" and "sell" orders are out at what prices, how much Bitcoin you could buy or sell right now and what the average price you could buy or sell a large quantity of Bitcoin at. (Eg, if you wanted to sell X Bitcoin, you might be able to sell X/2 Bitcoin at $PRICE and X/2 Bitcoin at $PRICE/2, for an average price of $PRICE*3/4.)
