TL;DR: A satoshi is the smallest unit of bitcoin recorded on the blockchain. One bitcoin equals exactly 100,000,000 satoshis, so a satoshi is 0.00000001 BTC. The unit is named after Satoshi Nakamoto, Bitcoin's pseudonymous creator, and is usually shortened to "sat" or "sats". Divisibility this fine means you never need to buy a whole bitcoin, wallet balances can be shown in sats instead of decimals, and network fees can be quoted precisely as satoshis per virtual byte.
Satoshi (sat): the base unit of account on the Bitcoin network, equal to one hundred-millionth of a bitcoin. Every amount the protocol records, from wallet balances to transaction fees, is stored as an integer number of sats. The "bitcoin" denomination is a human-friendly label applied on top: software multiplies and divides by 100 million for display, but the ledger itself only ever counts satoshis.
Bitcoin's Smallest On-Chain Unit
The Bitcoin protocol stores balances as whole numbers of satoshis, never as decimal fractions of a coin. Bitcoin Core defines the relationship in a single line: the COIN constant in src/consensus/amount.h sets one bitcoin equal to 100,000,000 satoshis. Even the famous 21 million supply cap is expressed in the code as 2,100,000,000,000,000 sats.
Working in integers is a deliberate engineering choice. Floating-point decimal arithmetic introduces rounding errors, and rounding errors in a monetary ledger are unacceptable. By counting indivisible base units, every node on the network computes identical amounts every time.
The name honors Satoshi Nakamoto, the pseudonymous creator who published the Bitcoin whitepaper in 2008 and launched the network in January 2009. The community settled on "satoshi" as the name for the smallest unit around 2011, and the shorthand "sat" has since become the everyday term. If you are new to how the network itself operates, start with What Is Bitcoin?
Bitcoin Units at a Glance
| Unit | Value in bitcoin | Value in satoshis | Where you see it |
|---|---|---|---|
| bitcoin (BTC) | 1 | 100,000,000 | Exchange prices, large balances |
| satoshi (sat) | 0.00000001 | 1 | Wallet balances, fees, Lightning payments |
| millisatoshi (msat) | 0.00000000001 | 0.001 | Lightning Network internal accounting only |
Other denominations such as millibitcoin (mBTC, one-thousandth of a bitcoin) appear in some older software, but everyday usage has consolidated around two units: bitcoin for large amounts and sats for small ones.
Why Divisibility Matters
Divisibility is one of the properties that makes a good money work, and bitcoin is among the most divisible monies ever created. Three consequences follow.
No one needs a whole coin. Newcomers frequently assume bitcoin must be bought one full unit at a time. That assumption is wrong. Any amount can be purchased, and most people accumulate in small increments. The protocol treats 5,000 sats with the same rigor as 5,000 bitcoin. Practical purchase routes are covered in How Do I Add Bitcoin to My Wallet?
The unit scales with adoption. A fixed supply of 21 million coins sounds small for a global monetary network until you count in sats: 2.1 quadrillion base units. If demand for bitcoin grows over decades, prices of everyday goods could simply be quoted in sats rather than in fractions of a coin. The supply cap limits the number of coins, never the number of people who can hold meaningful amounts.
Small payments stay precise. Fees, micropayments, and exchange order books all need finer resolution than a whole coin. Satoshi-level precision keeps a coffee-sized payment exact on a network that also settles billion-dollar transfers.
Sats on the Lightning Network
The Lightning Network, Bitcoin's payment-channel layer, takes divisibility one step further. Lightning balances are tracked in millisatoshis (msat), each worth one-thousandth of a satoshi. The Lightning protocol specifications denominate payment amounts in msat so that routing nodes can charge fees on tiny payments with fair precision.
Millisatoshis exist only inside Lightning's off-chain accounting. The Bitcoin blockchain cannot record anything smaller than one satoshi, so when a Lightning channel closes and settles on-chain, balances round to whole sats. You will see msat in Lightning invoices and node software, never in an on-chain transaction. For how the layer works end to end, see What Is the Lightning Network?
How Wallets Display Amounts
Wallets choose a denomination for display, and the choice changes how the same balance reads:
- 0.001 BTC and 100,000 sats are the same amount.
- 0.00025000 BTC and 25,000 sats are the same amount.
- 1.5 BTC and 150,000,000 sats are the same amount.
Many people find sats easier to read because the numbers are whole: "25,000 sats" parses at a glance, while "0.00025 BTC" invites miscounting zeros. The Blockstream app lets you set the denomination used across the interface, so balances and payment amounts can be shown in bitcoin or in sats, alongside an equivalent in your local currency. Checking that a received amount matches what you expected is simpler when the unit matches the size of the payment: sats for small transfers, bitcoin for large ones.
When in doubt, count the relationship out: move the decimal point eight places to convert between bitcoin and sats. 0.00000001 BTC is 1 sat; 0.1 BTC is 10,000,000 sats.
Reading Fees: What sat/vB Means
Satoshis are also the unit of Bitcoin's fee market. When your wallet estimates a fee, it quotes a fee rate in satoshis per virtual byte, written sat/vB. A virtual byte measures how much space a transaction consumes in a block, so the fee rate expresses what you are paying per unit of scarce block space, the way fuel is priced per liter rather than per trip.
A typical estimate might read "12 sat/vB". A simple transaction of around 140 virtual bytes at that rate pays 1,680 sats in total fees. When many transactions compete for the next block, the fee rate rises; when the mempool is quiet, it falls. Wallets translate this into the familiar high, medium, and low priority options by consulting current fee estimates. Why fees exist at all, and who receives them, is explained in Why Does Bitcoin Have Fees?
Knowing the notation protects you in practice. A fee rate of 12 sat/vB is modest; a fee rate of 500 sat/vB during quiet hours means something is misconfigured or a wallet default deserves a second look before you press send.
Thinking in Sats
The shift from whole-coin thinking to sat thinking changes how people relate to the asset. Unit bias, the instinct that owning one whole unit of something matters, pushes newcomers toward assets that cost less per coin regardless of the economics behind them. Counting in sats dissolves the bias: everyone is accumulating the same base unit, and the only question is how many.
Sats also make Bitcoin's long-term arithmetic concrete. Dividing the 21 million cap across the world's population leaves only about 260,000 sats per person if distributed evenly, with far less actually available once lost coins and long-term holders are counted. None of this predicts what a sat may be worth in the future, a question this article leaves alone. The arithmetic explains something narrower: why the smallest unit of bitcoin, rather than the whole coin, has become the everyday denomination of the network.
How many satoshis are in one bitcoin?
One bitcoin contains exactly 100,000,000 satoshis. The relationship is fixed in the protocol itself: Bitcoin Core defines the COIN constant as 100 million, and every amount on the blockchain is recorded as an integer number of satoshis, never as a decimal fraction of a bitcoin.
How much is one satoshi worth?
A satoshi is worth one hundred-millionth of whatever bitcoin trades at, so its fiat value changes continuously with the market. To convert, divide the current bitcoin price by 100,000,000. Wallets and exchanges display the conversion automatically, and prices are best checked on a regulated exchange at the moment of use.
Can I buy less than one bitcoin?
Yes. Bitcoin's divisibility means any budget can buy some amount of it, from a few thousand sats upward. The protocol sets no minimum purchase, though exchanges set their own minimum order sizes and on-chain transactions need enough value to be worth the network fee they pay.
What is a millisatoshi?
A millisatoshi (msat) is one-thousandth of a satoshi, used only inside the Lightning Network for routing accounting. Lightning tracks balances at msat precision so that tiny routing fees can be calculated fairly, but amounts settle back to whole satoshis whenever a channel closes on-chain.
Why is it called a satoshi?
The unit honors Satoshi Nakamoto, the pseudonymous creator who published the Bitcoin whitepaper in 2008 and mined the first block in 2009. The community adopted the name for the smallest unit around 2011, and "sat" became the everyday shorthand as smaller denominations grew more practical.