Well, let's say the US switches all of it's currency over to Bitcoin and it's the only country in the world that uses it. On September 2017, there was 1.58 trillion US dollars in circulation. Let's convert that into the 21 million Bitcoin that will ever exist. 1.58 trillion divided by 21 million is a bit more than 75,000 US dollars per Bitcoin. But Bitcoin is a global currency, imagine how high that number would be if it was converted into the value of all the currency in circulation in the world.