Satoshis (Sats): Bitcoin's Smallest Unit Explained
What is a satoshi? One sat is 0.00000001 BTC, Bitcoin's smallest unit. Learn the conversions, how fees in sat/vB work and why people count in sats.
A satoshi, or "sat", is the smallest unit of bitcoin recorded on the blockchain: one hundred-millionth of a bitcoin. In other words, 1 BTC = 100,000,000 sats, and 1 sat = 0.00000001 BTC.
Where the name comes from
The unit is named after Satoshi Nakamoto, the pseudonymous creator of Bitcoin. Nakamoto did not coin the term; it was adopted by early members of the community as a tribute and quickly stuck. Today "sats" is the everyday unit for small amounts, tips and fees.
Over the years there have been proposals to make other units the default display, such as "bits" of 100 sats, but none has become universal. Many wallets now let users switch between BTC and sats, and a growing number of apps show small balances in sats by default.
Internally, Bitcoin software never deals with fractional bitcoins at all. Every amount on the blockchain is stored as a whole number of satoshis, and "BTC" with eight decimal places is simply a display format. When a wallet shows 0.0005 BTC, the transaction underneath says 50,000.
Useful conversions
- 1 BTC = 100,000,000 sats
- 0.1 BTC = 10,000,000 sats
- 0.01 BTC = 1,000,000 sats
- 0.001 BTC = 100,000 sats (also called 1 mBTC)
- 0.000001 BTC = 100 sats (sometimes called 1 "bit", or 1 μBTC)
- 0.00000001 BTC = 1 sat
Some protocol numbers read more naturally in sats. The current block subsidy of 3.125 BTC is 312,500,000 sats. The 21 million BTC cap corresponds to about 2.1 quadrillion sats — 2,100,000,000,000,000 — and because the subsidy is calculated in whole sats and rounded down at each halving, the real total ends up slightly lower.
Sats and transaction fees
Fees are where sats matter most. They are quoted as a rate in satoshis per virtual byte (sat/vB), and the total fee is that rate multiplied by the transaction's size. A typical simple payment is around 140 vB, so at 2 sat/vB it costs roughly 280 sats; at 50 sat/vB the same payment would cost about 7,000 sats. At the time of writing (October 2026), median fee rates are very low, about 1–3 sat/vB. Our mempool guide explains how those rates are set, and the block feed shows the median fee of every recent block.
There is also a practical lower limit on outputs. Nodes treat outputs that would cost more to spend than they are worth as dust, and by default they do not relay transactions that create them. For common address types, the dust threshold is a few hundred sats.
Anything smaller than a sat?
On the base chain, no: one satoshi is the indivisible minimum. The Lightning Network, however, tracks balances in millisatoshis (thousandths of a sat) inside payment channels, which makes very small payments possible. When a channel is closed on-chain, balances are settled in whole sats. For on-chain users the satoshi is the final unit: every output and every fee must be a whole number of sats, with nothing below it.
Frequently asked questions
How many satoshis are in one bitcoin?
Exactly 100 million. That figure is part of the protocol and has not changed since 2009.
Why do people count in sats instead of BTC?
Because most everyday amounts are small fractions of a bitcoin. "2,500 sats" is easier to read and say than "0.000025 BTC", and it avoids mistakes with long strings of zeros.
Is a satoshi worth a fixed amount of money?
No. A sat is always 1/100,000,000 of a bitcoin, so its value in any currency moves exactly with the price of bitcoin.
FreeBTC is free to play and speaks in the units the network actually uses: blocks, pools and fee rates in sat/vB. Getting comfortable with sats makes the median-fee prediction in each round much easier to reason about. Try a round with the next block.