What is the smallest unit of Bitcoin called?

The satoshi is the smallest unit of Bitcoin.

One bitcoin is divisible into 100 million satoshis, so one satoshi equals 0.00000001 BTC. The unit is commonly abbreviated as “sat” or “sats,” especially when discussing fees, small payments, or Bitcoin balances below one coin. Its name honors Satoshi Nakamoto, the pseudonymous creator of Bitcoin.

Using satoshis lets the Bitcoin system represent tiny amounts without relying on ordinary decimal rounding. Bitcoin’s software records values in integer base units, which helps transactions remain precise. A payment of 25,000 satoshis, for example, is 0.00025 BTC.

The alternatives in this question belong to other contexts. Finney is an informal Bitcoin subdivision equal to 0.1 BTC, while wei is Ethereum’s smallest denomination and gwei is commonly used for Ethereum gas fees. Bitcoin’s current protocol supports eight decimal places, although future consensus changes could theoretically alter that limit.