This is a tough question, as it can be asnwered in two different ways: 1. how much value is held in the form of fiat currency, and 2. what is the value of all existing property and investment (as most of all the money in the world is invested in financial instruments, such as bonds, stocks, gold, and apartments). The 2nd one is, in my opinion, more relevant, and can be answered by evaluating how much money all these financial instruments are worth.
The asnwer to the first one is evaluated to be as high as 80trillion US$. That is: 80 000 000 000 000$.
The answer to the second question is much harder to evaluate, as there are so many forms of financial istruments. However, to give you an idea, some evaluations vary from 544trillion US$ to 1.2quadrillion US$. That is: 544 000 000 000 000 – 1 200 000 000 000 000$.