The unit model
One coloured satoshi is one unit, supply is measured in satoshis, and decimals are presentation only.
Protocol behavior Verified 2026-08-31
Describes the Atomicals protocol itself at the pinned reference revision. It does not promise that any product exposes it.
- Page ID
-
protocol/arc20/unit-model - Normative authority
- Atomicals reference implementation
- Networks
- mainnet
- Documentation version
- 2026.08
- Audience
- everyone, developer
- Owner
- bitcoin-universe-docs
- Sources
-
- Atomicals ElectrumX
at
v1.5.2.0 - Atomicals protocol guide
at
unversioned
- Atomicals ElectrumX
at
The rule
Section titled “The rule”One ARC-20 unit is one satoshi in an output a validator recognises as coloured for that token. Native quantities are integers. There is no smaller division.
What follows immediately
Section titled “What follows immediately”Supply is satoshis. A token with 100 000 000 units required 100 000 000 satoshis, which is one bitcoin, to exist. Large supplies are expensive by construction.
Dust limits apply. An output that Bitcoin will not relay cannot carry units. In practice a coloured output must be at or above the relay dust threshold for its script type.
Balances are sums, not stored values. A wallet total is the sum of the coloured outputs it can spend. Nothing on chain stores that total.
Spending is all or nothing per output. There is no partial spend. Moving part of a lot means building a transaction whose outputs receive the split you want.
Worked numbers
Section titled “Worked numbers”| Deployment | Mint amount | Max mints | Nominal maximum issuance | Bitcoin required |
|---|---|---|---|---|
| Small | 1 000 sats | 10 000 | 10 000 000 units | 0.1 BTC |
| Medium | 10 000 sats | 21 000 | 210 000 000 units | 2.1 BTC |
| Large | 100 000 sats | 21 000 | 2 100 000 000 units | 21 BTC |
Nominal maximum issuance is mint_amount * max_mints. It is a ceiling on what claims can produce,
not a promise that the ceiling is reached.
Decimals
Section titled “Decimals”decimals is optional metadata that tells a wallet how to format a number for a reader. A token
with 100 000 units and decimals of 2 may be displayed as 1 000.00. The chain still holds
100 000 integer units in 100 000 coloured satoshis.
Never divide a native quantity by a power of ten before doing arithmetic on it, and never let a formatted figure enter a transaction builder. See metadata and decimals.
Dust and safety
Section titled “Dust and safety”A coloured output near the dust threshold is fragile. Any transfer that needs to leave a remainder smaller than the threshold cannot place that remainder in a new output, so it burns.
Practical guidance:
- Keep lots at sizes that divide cleanly for the transfers you expect.
- Prefer a small number of larger lots over many dust-sized lots.
- Model any split before building it. See allocation visualizer.