Broadly, the money supply is made up of:
- Currency in circulation (cash held by the public)
- Checkable deposits (bank deposits that can be withdrawn by check or digital equivalent)
- Other deposits, such as savings deposits, money market deposits, and time deposits.
The correlation between government spending and an exact equivalent increase in the money supply is not direct or immediate. Money supply doesn't only depend on the amount of government spending but also other factors like private bank lending, central bank actions, and even international flows of money.
When the government spends, it adds reserves into the banking system. But what happens next can vary. Banks can lend out their excess reserves, creating more deposits and thus increasing the money supply. Or, they can choose to hold onto these reserves and not lend them out, in which case the money supply would not increase by the full amount of government spending.
Moreover, the central bank can also influence the money supply by conducting open market operations, which is essentially buying or selling government bonds. When the central bank buys bonds, it increases the reserves of banks, giving them more capacity to lend, which can increase the money supply. Conversely, if it sells bonds, it drains reserves from the banking system, potentially decreasing the money supply.
This is why we don't see a 1:1 correlation between government spending and changes in the money supply.
You can find these explanations in various economic textbooks, such as "Macroeconomics" by Paul Krugman and Robin Wells:
Amazon.com ......or in Federal Reserve resources like the one available at this link:
What is the money supply? Is it important?.