How is it Measured?

Sure, money is the $10 bill you lent to your friend the other day and don't expect back anytime soon. But exactly how much money is out there and what forms does it take? Economists and investors ask this question everyday to see whether there is inflation or deflation. To make money more discernible for measurement purposes, they have separated it into three categories:

• M1 – This category of money includes all physical denominations of coins and currency, demand deposits, which are checking accounts and NOW accounts, and travelers' checks. This category of money is the narrowest of the three and can be better visualized as the money used to make payments.
  
• M2 – With broader criteria, this category adds all the money found in M1 to all time-related deposits, savings deposits, and non-institutional money-market funds. This category represents money that can be readily transferred into cash.
  
• M3 – The broadest class of money, M3 combines all money found in the M2 definition and adds to it all large time deposits, institutional money-market funds, short-term repurchase agreements, along with other larger liquid assets.

By adding these three categories together, we arrive at a country's money supply, or total amount of money within an economy.

How Money is Created
Now that we've discussed why and how money, a representation of perceived value, is created in the economy, we need to touch on how the central bank (the Federal Reserve in the U.S.) can manipulate the money supply.

Among other things, a central bank has the ability to influence the level of a country's money supply. Let's look at a simplified example of how this is done. If it wants to increase the amount of money in circulation, the central bank can, of course, simply print it, but as we learned, the physical bills are only a small part of the money supply.

Another way for the central bank to increase the money supply is to buy government fixed-income securities in the market. When the central bank buys these government securities, it puts money in the hands of the public. How does a central bank such as the Federal Reserve pay for this? As strange as it sounds, they simply create the money out of thin air and transfer it to those people selling the securities! To shrink the money supply, the central bank does the opposite and sells government securities. The money with which the buyer pays the central bank is essentially taken out of circulation. Keep in mind that we are generalizing in this example to keep things simple. (For more information, see the Federal (the Fed) Reserve Tutorial.)

Conclusion
Remember, as long as people have faith in the currency, a central bank can issue more of it. But if the Fed issues too much money, the value will go down, as with anything that has a higher supply than demand. So even though technically it can create money "out of thin air," the central bank cannot simply print money as it wants.

Read more: http://www.investopedia.com/articles/basics/03/061303.asp#ixzz1U9mYQ3pb