Satoshi

A satoshi(often shortened to “sat” in slang) is the smallest indivisible unit of Bitcoin. One bitcoin equals exactly 100,000,000 satoshi. Named after Satoshi Nakamoto, the pseudonymous author of the 2008 Bitcoin whitepaper.

Bitcoin protocol stores all values as integer satoshi amounts. The 21-million BTC supply cap maps to exactly 2,100,000,000,000,000satoshi (2.1 quadrillion). That fits comfortably inside a 64-bit integer, which is why Bitcoin wallet software historically didn’t need BigInt the way Ethereum tooling does.

For micropayments and Lightning Network channels, satoshi is the natural denomination. Sub-satoshi units (millisatoshi, 1 msat = 10⁻³ satoshi) exist in Lightning for precise fee accounting but aren’t valid on the base Bitcoin chain.