A deceptively simple question
In the previous guide we settled what money is for — it is whatever does the three jobs of a [[functions-of-money|medium of exchange, a unit of account, and a store of value]] — and saw that modern money is [[commodity-vs-fiat-money|fiat]], valuable by convention rather than because it is made of gold. That tells us the role money plays. It does not yet tell us how much of the stuff is out there. Ask a central banker the apparently innocent question "how much money is there in the country?" and you will not get one number — you will get several, with names like M0, M1, and M2.
Why so slippery? Because the notes in your wallet are plainly money, and the apartment you own plainly is not — but in between sits a long ramp of things that are sort-of money. The balance in your checking account is money; you spend it every day without touching a coin. The balance in a savings account is almost money — a few clicks away from being spendable. A six-month deposit you cannot touch without a penalty is money-ish. Drawing the line anywhere is a judgement call, so statisticians refuse to draw just one. They publish a family of measures, the [[monetary-aggregates|monetary aggregates]], each a wider circle than the last.
Liquidity: the ruler that orders the aggregates
The hidden ruler that orders this ramp is [[liquidity|liquidity]] — how easily and cheaply an asset can be turned into spending power without losing value. Cash is the most liquid thing there is: it already is spending power, instantly, anywhere, at face value. A checking deposit is nearly as liquid. A savings account is a small step down. A house is deeply illiquid — selling it takes months, costs thousands in fees, and the price you get is uncertain. The aggregates are simply this same ramp sliced into bands: each wider M adds the next, slightly-less-liquid layer of assets to the ones already counted.
The nested rings: M0, M1, M2
Start at the hard centre. M0, also called the [[monetary-base|monetary base]] or base money, is the most basic, government-issued money: physical notes and coins, plus the reserves that commercial banks hold in their accounts at the central bank. This is the money the central bank itself creates directly — the raw material. Notice it already contains something you never spend: bank reserves are money banks hold, not money in your pocket. That is the first hint that "money" has layers an ordinary person never sees.
Now widen the ring. M1 is the money people can spend more or less immediately: currency held by the public (notes and coins outside the banks) plus the balances in checking and other demand-deposit accounts you can draw on at will. M1 deliberately drops bank reserves — those are not spendable by households — but adds in the vastly larger pool of bank deposits that ordinary people actually transact with. Then widen once more. M2 takes everything in M1 and adds near-money: savings deposits, small time deposits, and similar balances that are not quite spendable on the spot but convert to cash with little effort. Each circle sits inside the next: every dollar in M0 currency is also somewhere in M1, every dollar of M1 is inside M2.
Nested money (toy economy, $ billion):
M0 = notes & coins (everywhere) + bank reserves
= 100 + 150 = 250
M1 = currency held by public + checking deposits
= 80 + 520 = 600
(the other 20 of cash sits in bank tills)
M2 = M1 + savings + small time deposits
= 600 + 1,800 = 2,400
So: M0 < M1 < M2 (each ring contains the last)
Cash you can hold (80) is a tiny slice of M2 (2,400).Two warnings before you take M0, M1, M2 as universal law. First, the exact definitions differ by country and have been revised over time — the United States, the eurozone (which uses M1/M2/M3) and China each draw the boundaries a little differently, and what counts as "checkable" or "small" is a matter of convention. Second, the labels are not magic; M2 is not "more money" than M1 in some deeper sense, it is just a broader count that includes less-liquid stuff. The numbers answer different questions, not the same question with different precision.
Where does most money come from?
Look again at the toy numbers and a puzzle leaps out. The central bank directly created the M0 base of 250 — yet M2 is 2,400, nearly ten times larger. Where did the extra come from? Not from a printing press. The gap between narrow base money and broad money is created by [[commercial-bank|commercial banks]] in the ordinary course of lending. When a bank makes a loan, it does not hand over a sack of someone else's cash; it credits a new deposit into the borrower's account — and that deposit is brand-new M1 and M2 that did not exist a moment before. This is the surprising plumbing the next guides open up; for now, just notice that it must be happening, because the broad aggregates dwarf the base the state actually printed.
Why "how much money" is genuinely hard
So the original question — "how much money exists?" — has no single honest answer, and the reasons go deeper than messy definitions. Liquidity is a continuum with no natural cut point, so any boundary between "money" and "not money" is partly arbitrary. New money-like instruments keep appearing — money-market funds, prepaid cards, and now stablecoins and other digital balances — and statisticians must keep deciding which to fold in. The financial innovation of recent decades is exactly why central banks added and sometimes retired aggregates like M3.
There is even genuine debate among economists about which aggregate matters. For decades some argued that watching the money supply was the key to controlling inflation; in practice the link between any single M and prices proved loose and unstable, and most central banks today steer interest rates rather than targeting a money number directly — a debate the Monetary Policy rung will return to. None of this means the aggregates are useless. They are invaluable for seeing the structure of money, tracking how fast lending is expanding, and spotting trouble. The right lesson is humility: "the" money supply is a family of useful measurements, not a single fact of nature waiting to be read off a meter.
One last guard against confusion, carried over from the very start of this ladder: the money supply is not the nation's wealth. The aggregates count claims that function as money, not the houses, factories, skills, and resources that make a country rich. Recall the distinction between [[money-vs-wealth|money and wealth]] — printing more M does not create more real things to buy, it usually just raises their prices. Money is the plumbing; wealth is the water. Knowing how much money exists, and in what form, tells you about the plumbing — which, as the rest of this rung shows, is well worth understanding.