Based on the truth of money and interest rate, the price level is proportional to the currency volume. Therefore suppose two currencies BTC and USD are used in the same economy, meaning the set of transactions that people are willing to do in BTC is the same as the set of transactions that people are willing to do in USD, then by the following facts (at someday 2016 Jun):

• USD currency volume is 1.3817T
• BTC currency volume is 0.0000156982T

The BTC/USD exchange rate shall be 88016.46 which is far beyond the current BTC/USD exchange rate 680.39, not to mention that the USA will still print new money in the future indefinitely while BTC volume is capped at 21M. Further, BTC being a global currency that can apply to economy more than the USD economy, the number can even be higher. Ironically, the much lower level is suggesting that the BTC economy is currently much smaller than that of the USD.

See here for more quantitative explanation about the exchange rate K/K' * V'/V between two currencies. For example, currently the global M0 plus the gold can be treated as a single currency USD and with a total volume 15.3T. Suppose the economy of bitcoin reaches the size of all global M0 and gold, in other words, the energy power of bitcoin K reaching the same as the current money energy power of global economy K', then the exchange rate will be V'/V which is 729k. Further, this number does not speculate on the shift of energy power from K' to K due to energy conservation. If one speculates on the shift and the resulting depreciation of fiats, the exchange rate can be frightening.