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Sats

sat, satoshi, satoshis, millisat, millisats, millisatoshi, millisatoshis, msat, msats

Short for satoshis: one bitcoin contains 100,000,000 sats, and Lightning commonly tracks thousandths of a sat as millisats.

A sat, or satoshi, is one hundred millionth of a bitcoin: 0.00000001 BTC. Sat and sats are the everyday shorthand for satoshi and satoshis. On-chain outputs are denominated in sats, even if wallets choose to display balances in bitcoin or fiat terms. It is the real base unit defined in the original Bitcoin code.

Because one bitcoin contains 100,000,000 sats, small Bitcoin amounts are usually easier to read and talk about in sats. Saying "25,000 sats" is more natural than saying "0.00025 BTC". At OpenSats, both donations and grant payments are often described this way. They are still bitcoin amounts, expressed in the smaller unit.

Lightning goes one step smaller internally with millisatoshis, abbreviated msats. One sat equals 1,000 msats. Msats are useful for routing fees, channel accounting, and invoice precision, even though the network cannot transfer sub-millisatoshi amounts and on-chain settlement still resolves in whole sats. BOLT 11 invoices and Zaps often rely on this finer unit.

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