To make this question answerable, let's start by asking, "How much money is there in actual United States dollars?" Since the statistics for the U.S. are easy to come by, we can examine this question in a couple of different ways.
The first way to look at it might be, "How much cash is there in U.S. currency?" If you took all the bills and coins floating around today in the world and added them all up, how much money would you have? All that hard and easily liquidated currency is known as the M0 money supply or monetary base. This includes the bills and coins in people's pockets and mattresses, the money on hand in bank vaults and all the deposits those banks have at reserve banks [source: Hamilton]. According to the Federal Reserve, there was $5.8 trillion in the M0 supply stream as of March 2021, the most recent data available.
That sounds like an incredible amount, but think about it this way: According to the U.S. Census, there were 332,290,964 people alive in the U.S. in May 2021. If you took all the cash and divided it up equally, each person should have about $17,454 in cash on them (or stuffed under the mattress). Obviously, there's some money missing, but there's an easy explanation for that: The Federal Reserve says that at any given time, between one-half and two-thirds of the M0 money stock of U.S. dollars is held overseas.
The rest of the money is in bank accounts of various types, and the Federal Reserve has tracked these funds in three different values known as the M1, M2 and M3 money supplies. (M3 has since been dropped. More on that below.)
M1 represents all the currency outside the U.S. Treasury, Federal Reserve banks and the vaults of depository institutions. It also includes demand deposits at commercial banks (excluding those amounts held by depository institutions, the U.S. government, foreign banks and official institutions), the Federal Reserve float and other liquid deposits. In March 2021, the M1 money supply for U.S. dollars equaled about $18.7 trillion [source: Federal Reserve].
M2 is the M1 supply, plus small-denomination time deposits (less than $100,000). In March 2021, the M2 money supply was about $19.9 trillion [source: Federal Reserve].
M3 is M2 plus larger CDs. As of March 2006, the Fed stopped tracking the M3 money stock as an economic indicator because it felt it did not add any information on economic activity that was not already available from M2 [sources: Federal Reserve].
All told, anyone looking for all of the U.S. dollars in the world in May 2021 could expect to find approximately $19.9 trillion in existence, using the M2 money supply definition. If you just want to count the value of notes and coins, there are about U.S. $2.1 trillion worth of notes and coins floating around the globe [source: Federal Reserve].
But suppose you wanted to know the actual number of notes in circulation, rather than how much they were worth? At the end of 2020, the Fed estimated there were 50.3 billion notes (ranging from humble $1 bills to mighty $10,000 bills) in circulation. This information is updated annually.
So, now that we have figured out the U.S. money supply as much as we can, what about the rest of the world?