WHAT'S IN A NUMBER?

Theoretically, any element of Bitcoin’s design can be altered at any time, should a Bitcoin Improvement Proposal (BIP) receive sufficient community support. But more than any other element of Bitcoin’s design, the 21M cap feels sacrosanct. To change it would be to attack the very fundamentals that make Bitcoin so valuable. Any BIP attempting to do so would receive short shrift.

Bitcoin’s fixed supply is a cornerstone of its design, embedding digital scarcity into its DNA and setting it apart from inflationary fiat currencies. Unlike dollars or euros, which central banks can print endlessly, Bitcoin’s protocol enforces a hard limit, ensuring no more than 21 million coins will ever exist.

But what drove Satoshi Nakamoto to choose this exact figure? The best guess is that Satoshi made an educated guess – and at this stage in Bitcoin’s lifespan, it looks to have been a pretty good one. “I wanted to pick something that would make prices similar to existing currencies, but without knowing the future, that’s very hard,” he confessed in an email to Martti Malmi. “I ended up picking something in the middle.”

He added: “If Bitcoin remains a small niche, it’ll be worth less per unit than existing currencies. If you imagine it being used for some fraction of world commerce, then there’s only going to be 21 million coins for the whole world, so it would be worth much more per unit.”

The goal, then, was to ensure that if Bitcoin gained traction, its value per coin wouldn't skyrocket to absurdity – like trillions per BTC – or plummet to irrelevance. Picking a fiat currency against which to price your first-of-its-kind digital currency is as hard as it sounds, but if Satoshi envisioned 0.001 BTC equaling about 1 euro, Bitcoin has exceeded its creator’s expectations by multiples.

What’s clear is that Satoshi thought long and hard about the matter. As he elaborated in a May 2009 email to Martti Malmi, “If Bitcoin remains a small niche, it'll be worth less per unit than existing currencies. If you imagine it being used for some fraction of world commerce, then there's only going to be 21 million coins for the whole world, so it would be worth much more per unit.

“There's plenty of granularity if typical prices become small.  For example, if 0.001 is worth 1 Euro, then it might be easier to change where the decimal point is displayed, so if you had 1 Bitcoin it's now displayed as 1000, and 0.001 is displayed as 1.”

The Lore and Lure of 21

Beyond the code enshrined in Bitcoin’s protocol and Satoshi’s explanatory emails, the number 21 has become synonymous with Bitcoin, inspiring a cottage industry of numerological theorists. One popular idea ties it to gold, given that the total mined gold in history forms a cube roughly 21 metres on each side (about 9,261 cubic meters), symbolising Bitcoin as digital gold with comparable scarcity.

Economically, some argue that 21 million aligns with human psychology around currency valuation. With 100 million satoshis per bitcoin, the total supply equals 2.1 quadrillion satoshis – enough for global wealth distribution without tiny fractions feeling cumbersome.

Wilder speculations abound. The blackjack theory posits Nakamoto, a presumed gambler at heart, chose 21 to evoke the perfect hand in the classic card game. Another nods to Douglas Adams’ The Hitchhiker’s Guide to the Galaxy, where 42 is the “answer to life, the universe, and everything,” halved to 21 to denote Bitcoin’s emissions schedule. Less whimsically, it might reference 2008’s U.S. M1 money supply (around $1.4 trillion), scaled so that 21 million BTC could absorb similar value at parity.

These theories, while entertaining, highlight a truth: the exact “why” may forever elude us. What matters is the outcome – a protocol so robust that 21 million has become synonymous with trustless money. Bitcoin’s 21 million cap isn't just a limit, therefore – it’s a promise of predictability in an unpredictable world.

The concept of “Infinity Day” was introduced by Knut Svanholm on 21/08/21 as a symbolic celebration of the ethos driving Bitcoin. He noted that when you write the date 8/21, the “8” resembles the infinity symbol (∞), and the “21” refers to Bitcoin’s capped supply of 21 million coins. Thus, ∞/21M captures the idea of “all value” divided by the finite number of bitcoins — a gesture toward scarcity, value and long-term holding rather than short-term selling.

Whether born of math, metaphor, or mischief, this scarcity has propelled Bitcoin from obscurity to a multi-trillion dollar asset class. It is digital gold for the internet age, finite, fair, and forever 21 million strong.