Bitcoin (unit of currency)

As a unit of currency, "bitcoin" refers to the divisible accounting unit built into the Bitcoin protocol rather than the network itself: every balance on the blockchain is ultimately a count of the smallest indivisible piece, and one whole bitcoin is defined as exactly 100,000,000 of those pieces. This fixed ratio is hardcoded into Bitcoin's consensus rules and cannot be changed without breaking compatibility across the entire network.

The protocol stores and processes all values internally in satoshis, only converting to the familiar "1 BTC" format for human-readable wallets and exchange displays. Because bitcoin's market price has climbed well beyond what most people can afford to buy a whole unit of, smaller denominations have become common in everyday use: a sat is shorthand for satoshi, while a millibitcoin equals one thousandth of a bitcoin, or 100,000 satoshis. Other named fractions, such as microbitcoin and centibitcoin, exist but see far less real-world use than the sat.

This granularity matters for practical reasons. Bitcoin's total supply is capped at 21 million coins, so as adoption grows and each unit becomes scarcer, dividing it into smaller pieces keeps everyday payments workable rather than forcing users to transact in tiny decimal fractions of "1.0" bitcoin. It is especially visible on the Lightning Network, where near-instant micropayments are typically priced and displayed in sats rather than BTC, and where an even smaller unit, the millisatoshi, exists purely for internal fee calculations.