What Is a Satoshi? The Smallest Bitcoin Unit Explained

What a satoshi actually is

A satoshi is not a currency of its own and not a token. It is a subunit of bitcoin, the way a cent is a subunit of the euro. The difference is how fine the division goes: one euro has 100 cents, one bitcoin has 100 million satoshis.

This split is not just a display convenience, it is built into the software. The Bitcoin Core source code defines one BTC as 100,000,000 satoshis, and it holds amounts as whole satoshi numbers. The figure you see in bitcoin, with eight decimal places, is essentially the converted, human readable form of that.

Converting between bitcoin and satoshis

The conversion is just a decimal shift, because 100 million is a clean power of ten. From bitcoin to satoshis you move the decimal point eight places to the right, and eight places to the left the other way.

• 1 BTC is 100,000,000 satoshis.
• 0.001 BTC is 100,000 satoshis.
• 0.00005 BTC is 5,000 satoshis.
• 1 satoshi is 0.00000001 BTC.

A satoshi has no fixed money value. What one satoshi is worth in your currency is simply the current bitcoin price divided by 100 million, so it moves all the time. How much bitcoin swings and how to think about that is covered in is Bitcoin too volatile.

When you buy a small amount for the first time, many providers show it in sats anyway. How buying works, using Austria as the worked example, is covered in how to buy Bitcoin in Austria.

The Bitcoin units side by side

Besides BTC and satoshi you will run into a few in between units. They all describe the same thing at different levels of detail. The overview below shows the exact value and where each unit typically shows up.

The definitions of the in between units are set out in BIP-176, which fixes the term bit as 100 satoshis. For the Lightning Network, the Lightning specification (BOLT 2) states that amounts there are counted in millisatoshis, while only whole satoshis can be enforced on the blockchain.

Bits, sats and the ₿ symbol

There is a mix-up going around that is worth clearing up before you misread an amount. You will often see the claim that bits and sats are the same thing under two names. That is not quite right.

The motivation is easy to follow. Because a whole bitcoin has risen so far against euros and dollars over the years, many newcomers came away thinking they had to buy a whole one. Whole numbers instead of long decimals are meant to dissolve that. BIP-177 is explicit that using the ₿ symbol for base units is optional.

Practically, this means one thing for you: check which unit your wallet is currently set to before you send an amount. The value does not change, only the way it is written.

How many satoshis there are in total

From 21 million bitcoin and 100 million satoshis per bitcoin you get an arithmetic ceiling of 2,100,000,000,000,000 satoshis, or 2.1 quadrillion. That number is often quoted as if it were the exact final supply. The source code is more careful here.

In the Bitcoin Core source code the software rejects any amount above that ceiling as invalid. The comment next to it explicitly calls the value a sanity check rather than the actual money supply. According to the same comment, the amount that will ever really exist is a little below 21 million bitcoin, for several technical reasons. New satoshis enter circulation through the block reward. The mining guide shows how new bitcoin are created and why issuance shrinks over time.

Where the name comes from

The unit is named after Satoshi Nakamoto, the pseudonym under which bitcoin was published as a concept in 2008 and launched as software in 2009. Whether that was one person or a group has never been established. The earliest bitcoin source files still carry the authorship note under that name.

The use of satoshi for the smallest unit does not come from an official document. It settled into common use in the early community and has been used consistently ever since, including in technical specifications. The short form sat took hold mainly for small amounts and for saving.

What the small unit is good for

A division this fine has a practical reason. When a single bitcoin carries a lot of purchasing power, everyday amounts would be long, awkward decimals without smaller units. In satoshis the same figure can be written as a tidy whole number.

• Small amounts stay readable. 2,500 satoshis is easier to read than 0.000025 BTC.
• Regular saving feels more concrete when you think in fixed sat amounts rather than many decimal places. More on that in the section on building a position gradually.
• Network fees are usually quoted in satoshis, normally in relation to the size of the transaction.
• In the Lightning Network very small payments are normal, and there the accounting is done in millisatoshis. How to use Lightning in practice is covered in the use Bitcoin section.

On the Bitcoin blockchain itself the satoshi is the smallest unit. Millisatoshis exist only as a unit of account inside Lightning; for settlement on the blockchain amounts are rounded to whole satoshis. For bitcoin itself to become more divisible, the protocol rules would have to change, and no such change exists today.

Why a satoshi is not a separate coin

A common misunderstanding is that a satoshi is a separate, cheaper cryptocurrency you could buy instead of bitcoin. It is not. A satoshi is only a way of measuring an amount within bitcoin. Someone holding 10,000 satoshis holds 0.0001 bitcoin, not one unit of something else.

There are unrelated cryptocurrencies and tokens that use the name satoshi or the ticker SATS. These are technically not bitcoin and should not be confused with it. If a trading platform lists something called SATS, it is worth checking closely whether it means the bitcoin unit or a separate project.