Satoshi
In plain English
The smallest unit of bitcoin — one hundred-millionth of a BTC. Named after Bitcoin's pseudonymous creator, Satoshi Nakamoto.
What is a satoshi?
A satoshi, often shortened to "sat", is the smallest amount of bitcoin the network can record: 0.00000001 BTC. One bitcoin contains 100 million satoshis. The unit is named after Satoshi Nakamoto, the pseudonym of Bitcoin's still-unidentified creator.
Why bitcoin needs small units
Bitcoin's supply is capped at 21 million coins, so as demand grows, one whole BTC becomes an awkwardly large unit for everyday amounts. Divisibility solves this. Just as a dollar splits into cents, a bitcoin splits into satoshis — except far more finely, with eight decimal places rather than two.
This is why the common worry "I cannot afford a whole bitcoin" misunderstands how it works. You can buy a few thousand satoshis just as easily as a fraction of a share.
Where you will see sats
Satoshis appear wherever amounts are small. The Lightning Network, used for fast low-value bitcoin payments, prices almost everything in sats. Bitcoin transaction fees are quoted in satoshis per virtual byte (sat/vB), which is how wallets let you choose how much to pay for block space.
Some people also track "sats per dollar" — how many satoshis one dollar buys — as an alternative way of reading the exchange rate.
A note on other units
Bitcoin also has intermediate units such as the millibitcoin (0.001 BTC) and microbitcoin (0.000001 BTC), but these are rarely used. In practice you will encounter BTC and sats, and almost nothing in between.