What an unspent output is
A Bitcoin address does not hold one balance. It holds separate pieces of bitcoin called unspent outputs, often written UTXO. Each output paid to the address and not yet spent is one piece. A transaction can create more than one output. The balance is their sum.
What the note says
The Unspent outputs note counts those pieces. One of four lines appears:
- Good
3 unspent outputs. Fees depend on which outputs a transaction spends.
- Good
7 unspent outputs. Not highly fragmented.
- Warning
27 unspent outputs. Spending many separate outputs together can cost more in fees than spending fewer, larger outputs.
- Attention
80 unspent outputs. This address holds many separate coins. Spending them together can cost more in fees than spending fewer, larger coins.
Up to ten pieces reads Good. Eleven to fifty reads Warning, and more than fifty reads Attention, because of what a spend would cost.
What it means
A transaction has to name every piece it spends, and the network fee is paid for the size of the transaction, not for the amount sent. Spending twenty small pieces makes a bigger transaction than spending one large piece of the same value, so it costs more. Many pieces usually mean the address received many separate payments: mining payouts, exchange withdrawals or regular small purchases.
What it does not mean
It says nothing about the bitcoin itself. Each piece is as spendable as any other, and the count ignores value: fifty tiny pieces and fifty large ones read the same. It is not a judgment of whoever controls the address.
What you can do
Nothing is required. People who control an address sometimes combine many pieces into one when fees are low, which is an ordinary transaction from their own wallet. satoshis.watch only reads the chain and cannot do it for anyone. If you are watching an address, the note tells you what a future spend from it may cost.
Common questions
Is an unspent output the same as a coin?
Close enough. People say coin for a piece of bitcoin that can be spent on its own. The chain calls it an output of an earlier transaction that has not been spent yet.
Why does the count go up and down?
An incoming payment can add one or more pieces. A spend removes the pieces it used and often sends one new piece back as change. See what a change output is.
Can I see the individual pieces?
Yes. The address report lists each unspent output with its amount and the transaction that created it.