A Satoshi is the smallest fraction of a Bitcoin that can currently be sent: 0.00000001 BTC, that is, a hundredth of a millionth BTC.In the future, however, the protocol may be updated to allow further subdivisions, should they be needed. Further examples of units. 1  1 BTC = 1,000 mBTC (millibitcoin). Satoshi is the smallest fraction of a Bitcoin that can currently be sent: 0.00000001 BTC, that is, a hundredth of a millionth BTC. In the future, however, the protocol may be updated to allow further subdivisions, should they be needed. Further examples of units.