Dust

The line moves with the fee market rather than sitting at a fixed number. Spending one native SegWit coin takes about 68 virtual bytes, so a 5,000 satoshi coin is perfectly spendable at 10 sat/vB and worthless at 80 sat/vB. Most dust in ordinary wallets is not an attack, it is leftover change nobody planned.

How it works

Whether a coin counts as dust is a division problem you can do in your head.

Take the coin's value, divide by the size of the input that will spend it, and you get the fee rate at which it breaks even. For a native SegWit coin, that size is about 68 virtual bytes. A 546 satoshi output dies above roughly 8 sat/vB. A 5,000 satoshi output survives to about 73 sat/vB. A 10,000 satoshi output holds its value up to about 147 sat/vB, which covers all but the worst fee spikes. Older legacy inputs are more than twice as large, so the same amount sitting at an address starting with 1 becomes uneconomic at less than half the fee rate.

Nothing is lost, and nothing is broken. A dust coin stays valid forever and becomes spendable again the moment fees fall, which is the practical reason not to panic about it. The other way to recover it is to include it in a transaction you were making anyway: it adds its 68 virtual bytes to the cost, but it is not paying for a whole transaction on its own.

Wallets handle the awkwardness quietly. When the change from a payment would land below the relay threshold, Bitcoin Core and most other wallets drop the change output and hand that amount to the miner as extra fee, because creating an output nobody can afford to spend helps no one.

Where you see it

Dust accumulates from perfectly normal activity, which is why nearly every long-used wallet has some.

Change is the biggest source: pay 0.00987 BTC out of a 0.01 BTC coin and the remainder is a scrap. Exchange withdrawals leave crumbs behind when a rounding rule or a withdrawal fee shaves the amount. Lightning channel closes can return small on-chain balances. Airdropped advertising, tiny payments carrying a message or a link, arrives unrequested. Inscription and token experiments leave behind outputs held at the minimum the network will relay.

The sensible routine has three steps. Label each small coin when it appears, so you know later what it was. Leave it alone rather than paying a premium to move it. Then, during a genuinely cheap window, sweep the ones you can explain into a consolidation along with your other coins, which recovers the value at a marginal cost of a few hundred satoshis. Coins you cannot explain should stay frozen indefinitely, since the cost of leaving them is zero and the cost of spending them may be your privacy.

Dust vs a dusting attack

Dust describes a condition of a coin; a dusting attack describes an intent behind one. The overwhelming majority of small coins in a wallet are self-inflicted change and rounding leftovers, with nobody watching them at all. A dusting attack is a stranger deliberately sending you a scrap in the hope that your wallet will spend it beside coins they cannot otherwise connect to you. Since the correct response to both is the same, freeze it and label it, the distinction matters less in practice than the arithmetic does.