What is crypto market cap? The most misread number in crypto

On 19 February 2021, bitcoin's market value ticked past $1 trillion for the first time, and the headlines lined it up against Facebook and Tesla, both of which it had just passed, not bad for something that started life twelve years earlier as a nine-page whitepaper.

The part that never makes the headline is that nobody counted a trillion dollars that day, because no vault held it and no auditor signed it off, a price crossed a line and a multiplication ran and the headline wrote itself. That multiplication is market cap, the most quoted and least interrogated figure in crypto, and this guide is about how to read it without being fooled. It is an explainer, not financial advice.

The whole calculation fits in one line

The cap is just the last traded price multiplied by the circulating supply, so on that February day the sum was roughly 18.6 million bitcoin in circulation at a last price of about $53,800, run through a formula borrowed from the stock market, where it prices a company's shares.

Its one job is telling you how big one coin is next to another, and it does that job fast. Every price tracker ranks coins by it, bitcoin dominance, bitcoin's share of all crypto value, is built from it, and that share has sat around half in recent years, so the number earns its keep.

The trouble starts when people read the number as a pile of money, as if the whole sum were sitting in an account somewhere waiting to be spent.

Nobody invested the market cap

Price is set by the most recent trade, and the cap multiplies that one trade across every unit in existence, including coins that have not moved since 2010. Buy £50 of bitcoin through an on-ramp (Banxa has run that fiat-to-crypto plumbing since 2014) and £50 changes hands. Every other coin on the ledger gets re-marked for free. The money that actually moved can be a rounding error on the value that appeared.

It cuts the other way as well, and May 2022 remains the brutal example, when TerraUSD, an algorithmic stablecoin, lost its dollar peg, and between 9 and 13 May roughly $40 billion of market value attached to it and its sister coin LUNA evaporated. Nobody withdrew $40 billion, because there was never $40 billion in a vault to withdraw. There were tokens marked at prices that stopped being true, and when the marks fell, the paper value went with them.

A cap can double or halve while the actual cash changing hands stays modest, because the cap is a mark on paper, and nobody has to move any money to move a mark.

Unit bias: why the £0.001 coin is not cheap

A token priced at a fraction of a penny feels like a lottery ticket. Twenty pounds buys twenty thousand units, and the dangerous sentence arrives on cue: it only needs to reach a pound. Except a thousandfold price rise means a thousandfold cap rise. A coin already carrying a £400 million cap would need to reach £400 billion, over a third of bitcoin's value on its trillion-dollar day, for the penny dream to land.

Supply is the half of the sum people skip. Shiba Inu launched in August 2020 with a supply counted in the hundreds of trillions of units. At well under a penny per token in October 2021, it still carried a market value in the tens of billions of dollars, briefly cracking the top ten coins by size, and price told you nothing on its own. It never does.

Float games and the supply you cannot see yet

Circulating supply counts the coins available today, but plenty of projects hold back a large share for the team, early investors and the treasury, released on a timetable stretching years. XRP shows the scale that gap can reach: 100 billion units were created at launch in 2012, and for years only around half circulated, with tens of billions parked in escrow that has released on a monthly schedule since December 2017.

Fully diluted valuation, FDV, prices in the lot, meaning today's price multiplied by every token that will ever exist, and it matters because a token can list with just 5 per cent of its supply floating. Price discovery happens on that sliver, the FDV lands in the billions, and the other 95 per cent arrives later on a vesting schedule, whether anyone wants it or not. New listings in 2021 and again in 2024 repeated the pattern often enough that 'low float, high FDV' became its own complaint. A wide gap between cap and FDV is not a scandal so much as a delivery schedule, and the deliveries are supply.

A price only a spreadsheet believes

But the whole multiplication leans on one assumption, which is that the last price means something. On a token trading a few thousand pounds a day, one keen buyer sets the mark for every unit in existence, and the tracker prints a cap in the millions off the back of a single trade. Try to sell real size into that market and the price collapses long before the paper value reaches your account. Liquidity, the depth of real buyers and sellers, decides what a cap is actually worth, and thin markets print fat numbers.

The cartoon version arrived in 2021: a token themed on the Squid Game TV show, with no connection to the show, printed a vertical chart and a quoted price in the thousands of dollars, while most holders found its design blocked them from selling. On 1 November 2021 the developers cashed out a few million dollars, the price hit a fraction of a cent within minutes, and every cap computed from that quoted price had been fiction all the way up.

Why the same coin shows three different caps

Trackers disagree about what counts as circulating, because somebody has to decide whether locked tokens count, whether escrowed tokens count, and what to do with coins presumed lost or held by a foundation. CoinMarketCap has made those judgement calls since 2013 and CoinGecko has made its own since 2014, and the two do not always land in the same place, which is why one coin can wear a different cap on each site.

Supply itself needs care too, because the coins circulating now are not the same number as the total already minted, and neither is the maximum that can ever exist. Bitcoin's maximum is fixed at 21 million while Ethereum has no hard cap at all, and you cannot read either fact off a price, even though both change what the multiplication means.

What the number is actually for

Market cap ranks things, it does not value them. It will tell you bitcoin is the biggest asset in crypto and a new token is a minnow, and it is genuinely good at that one job. It cannot tell you whether anything is worth its mark, what was paid for it, or what you could get back out.

By December 2024, bitcoin's price had crossed $100,000 and the headline cap stood at roughly double that first trillion, still built the way it was built in 2021, from the last trade and the count of coins. The number grew and the measurement never did.

Read it the way you read a queue outside a restaurant, because the length of the queue tells you how popular the place is and nothing whatsoever about the cooking, and the trouble only ever starts when somebody mistakes the queue for the meal.