What Is a Satoshi? Bitcoin Units Explained

Bitcoin can be divided into very small fractions. The smallest indivisible unit is called a satoshi, named after Bitcoin's pseudonymous creator, Satoshi Nakamoto.

The Bitcoin Unit Hierarchy

Unit	Symbol	Value in BTC	Value in Satoshi
Bitcoin	BTC	1	100,000,000
Millibitcoin	mBTC	0.001	100,000
Microbitcoin	μBTC	0.000001	100
Satoshi	sat	0.00000001	1

One bitcoin equals exactly 100 million satoshi (10^8, or one hundred million). This is a fixed constant defined in Bitcoin's protocol and cannot be changed.

Why Satoshi Matters

When Bitcoin was created in 2009, 1 BTC was worth a fraction of a cent. The satoshi unit allowed for very small transactions without requiring fractional notation like 0.00000001 BTC.

As Bitcoin's price grew to thousands of dollars per BTC, satoshi became a natural unit for:

• Transaction fees — Network fees are expressed and calculated in satoshi (often as satoshi per byte of transaction data)
• Lightning Network payments — The Lightning Network uses millisatoshi (1/1000 of a satoshi) for routing fees
• Micropayments — Services that charge small amounts per action express prices in satoshi

Converting Between Units

1 BTC = 100,000,000 sat
1 mBTC = 100,000 sat
1 BTC = 1,000 mBTC

To convert BTC to satoshi: multiply by 100,000,000
To convert satoshi to BTC: divide by 100,000,000

Example: 0.005 BTC in satoshi:

0.005 × 100,000,000 = 500,000 sat

The 21 Million Supply Cap

Bitcoin's total supply is capped at 21 million BTC. In satoshi, that is:

21,000,000 × 100,000,000 = 2,100,000,000,000,000 sat

That is 2.1 quadrillion satoshi — a large number, but fixed and finite.

Bitcoin Is Divisible by Protocol

The 8 decimal places of divisibility are enforced at the protocol level. Every on-chain transaction stores amounts as integer satoshi values — there is no concept of a fractional satoshi in Bitcoin's base layer. The Lightning Network extends this with millisatoshi for routing, but these do not settle on-chain directly.

Sats vs Dollars

With Bitcoin at $50,000 per BTC, one satoshi equals $0.0005 (half a cent). At $100,000 per BTC, one satoshi equals $0.001 (one tenth of a cent). This makes satoshi a practical unit for small denominations as the Bitcoin price grows.

Many Bitcoin-native applications now quote prices in satoshi (sats) rather than BTC for clarity with small amounts.