There are less than 13 000 000 bitcoins availlable but not all are in circulations. Currently with the price of bitcoin circling at $600 US it's total value is about $7.8 Billion US. {If my calculations are correct}
As Bitcoin Jesus said in that article, there are not enough bitcoins to give each person in the UK even 1. {If you consider, that the monthly salary of the average UK worker is way above the current value of bitcoins, you would need to push the price per bitcoin up by 10 times, just to cover wage benefits, and that would amount to a bitcoin price of $ 6000 US per bitcoin.}
Then multiply that with 1000 if other countries also adopt bitcoin as a alternative and you get to a bitcoin price of $ 60 000 per bitcoin. {Now salaries are covered, what about the rest}
These are gross over exageration of figures, just to make a point, as to what has to happen, if bitcoin are accepted as a fiat substitute.
Think of it as 1.3 quadrillion. I paid 0.034 BTC for take-out the other day, Bitpay seem to be happy with the bit pennies I gave them