What Is a Satoshi? Bitcoin’s Smallest Unit Explained

A satoshi, or sat, is one hundred-millionth of a bitcoin: 0.00000001 BTC. It is the smallest amount the Bitcoin blockchain can record, so 100,000,000 sats make one whole coin. Wallet balances, network fees and Lightning payments are all, underneath, counts of satoshis.

This guide covers where the unit comes from, how the protocol stores it, and the places sats matter in practice. For quick conversions between sats, bits, mBTC and BTC, use the WishCoin converter.

Key numbers

Where the name comes from

Bitcoin was described in a 2008 white paper published under the name Satoshi Nakamoto, and its network started on 3 January 2009 with the genesis block. The creator’s real identity has never been confirmed. Early users on Bitcoin forums wanted a word for the tiniest fraction of a coin, and honouring the pseudonymous founder won out. Today “sat” and “sats” are the everyday short forms, and the slang “stacking sats” means buying small amounts regularly.

Nakamoto did not set out a naming scheme for units. What the original software did fix was the precision: amounts were stored as whole numbers, and one coin was defined as 100,000,000 of them. The name came later; the unit itself existed from day one.

How Bitcoin stores amounts

Inside a transaction, each output carries a value field holding a 64-bit integer. That integer is a count of satoshis, never a decimal fraction of a bitcoin. Bitcoin Core, the reference implementation, defines a constant called COIN equal to 100,000,000, and converts to BTC only when it shows an amount to a person.

Integer storage avoids rounding errors. Floating-point maths on computers cannot represent many decimals exactly, which would be a disaster for a ledger. By counting whole sats, the network guarantees that inputs and outputs add up precisely.

A direct consequence: nothing smaller than one satoshi exists on-chain. A wallet asked to pay 0.000000015 BTC must round to 1 or 2 sats.

The block subsidy in satoshis

New bitcoin enters circulation through the block subsidy, which halves every 210,000 blocks. Expressing it in sats shows how the schedule works.

Each halving divides the sat count by two and rounds down. After enough halvings the subsidy falls below one satoshi and becomes zero, which is why total supply ends slightly under 21 million coins. That point is expected around the year 2140.

Sats and transaction fees

Miners pick transactions by fee rate, measured in satoshis per virtual byte (sat/vB). Size, not value, decides the cost: sending 10,000 sats or 10 BTC costs the same if both transactions take up the same space.

Worked fee example

Take a simple payment with one SegWit input and two outputs, which comes to roughly 141 vB. At a fee rate of 4 sat/vB, the fee is 141 × 4 = 564 sats. Should the mempool get busy and the rate climb to 25 sat/vB, the same transaction costs 3,525 sats. In BTC, those fees are 0.00000564 and 0.00003525, which shows why people quote fees in sats.

Rates can now go below 1 sat/vB. Bitcoin Core 29.1, released on 4 September 2025, lowered its default minimum relay fee to 100 sats per thousand virtual bytes, or 0.1 sat/vB. The release notes warn that such low-fee transactions may not propagate until most of the network uses the new defaults.

Dust: when sats are too small to spend

An output worth less than it would cost to spend is called dust. Bitcoin Core’s default policy refuses to relay transactions that create outputs below a dust threshold, calculated from a dust relay fee of 3 sat/vB. For a legacy P2PKH output the threshold is 546 sats; for a native SegWit P2WPKH output it is 294 sats.

These are relay rules, not consensus rules, so a miner could still include such an output. In practice, wallets avoid creating dust, and many hide tiny unsolicited deposits, since “dusting” is sometimes used to try to link addresses.

Millisatoshis and Lightning

The Lightning Network moves payments through channels off the main chain, and its specifications (the BOLTs) count value in millisatoshis: 1 msat is a thousandth of a sat. Finer accounting lets routing nodes charge proportional fees on very small payments.

Lightning invoices encode amounts with letter multipliers defined in BOLT 11: m (milli), u (micro), n (nano) and p (pico) of a bitcoin. An invoice that starts lnbc2500u asks for 2,500 microbitcoin, which is 0.0025 BTC or 250,000 sats. With the n multiplier, 1n equals 100 msat, a tenth of a sat.

Millisatoshis never reach the blockchain. When a channel closes, balances settle in whole satoshis, and amounts too small to form an economic output are left out of the closing transaction.

Turning sats into BTC and back

Because one coin holds exactly a hundred million sats, conversion is a matter of shifting the decimal point eight places. Here are three cases worked through:

1. From sats to BTC. Take 73,500 sats. Write it with eight digits after a leading zero, 0.00073500, then trim the trailing zeros: 0.000735 BTC.
2. From BTC to sats. Take 0.3 BTC. Fill out the decimals to 0.30000000, drop the leading “0.” and you have 30,000,000 sats.
3. From msat to sats. A Lightning routing fee of 1,850 msat divided by 1,000 gives 1.85 sats. On-chain, that figure could not exist; only inside a channel can fractions of a sat be tracked.

Errors creep in when zeros are counted by eye. Counting digits in groups of three from the decimal point, then adding two more, gives a quick sanity check on any eight-place figure.

How wallets display sats

Most modern wallet apps include a setting to show balances in sats rather than BTC, and Lightning wallets often default to sats because payments there tend to be small. Exchanges, by contrast, usually quote and settle in BTC with eight decimals. Whichever view you pick, the balance on the blockchain is the same integer; only the label on screen changes.

A feel for common sat amounts

No fiat values appear here on purpose. A sat’s worth in dollars or euros moves with the market, while the counts above never change.

Writing sat amounts clearly

• Use whole numbers with thousands separators: 25,000 sats, not 25000.
• Write “sats” for plural amounts and “sat” for one, or for rates such as sat/vB.
• When a reader may be new to the unit, add the BTC equivalent once: 25,000 sats (0.00025 BTC).
• Avoid mixing units in one sentence; convert everything to sats or everything to BTC.

Frequently asked questions

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