A boat is a UTXO
Each UTXO is a fixed amount of bitcoin created by an earlier transaction and locked to your keys. Your balance is the sum of every boat in your harbour.
A nautical guide to UTXOs
Every coin is a boat.
Your wallet isn't one balance. It's a harbour full of boats of different sizes — each one an unspent transaction output, or UTXO. Paying someone means sailing whole boats out.
Open the harbourReading the chart
You sail out whole boats
You can't spend half a boat. A payment takes whole boats as inputs and launches new ones: one for the person you pay, and usually a change boat back to you.
Harbour fees are charged by weight
Fees depend on a transaction's size in virtual bytes, not on the amount. Every extra boat you sail out adds weight, so many small boats cost more to move than one big one.
Dust can't leave the harbour
A boat is dust when the fee to sail it out is bigger than the cargo it carries. Dust depends on the fee rate: a boat that's fine today can become dust when fees rise.
Harbour simulator
Choose a payment and a fee rate, pick boats yourself or let a strategy choose, then set sail and watch the harbour change. Sizes assume native SegWit: 68 vB per input, 31 vB per output, plus 10.5 vB of overhead. The boats and their amounts are examples.
sats
sat/vB
Harbour rules
Consolidate in calm water
When fees are low, sailing many small boats into one bigger boat makes later payments cheaper. It costs a fee now.
Merging links boats
Boats that sail out together are publicly linked as belonging to the same owner. If privacy matters, don't merge boats from different sources.
Name your boats
Many wallets let you label UTXOs and choose them by hand ("coin control"). Labels make it easier to decide which boats to sail.
Mind the change
Change boats come back to your harbour. A wallet may skip tiny change and add it to the fee instead, because it would cost more to spend later than it's worth.