The native unit of the Bitcoin protocol is the satoshi. All output values in Bitcoin transactions are expressed in complete numbers of satoshis. Bitcoin’s protocol doesn’t use any non-integer values for consensus related knowledge. Subsequently, the atomic unit of worth within the Bitcoin protocol is the satoshi.

The Lightning Community makes use of millisatoshi (1 sat = 1000 msat) for all values pertaining to channel updates: e.g. channel balances, HTLC quantities, forwarding charges, and bill quantities. Since millisatoshis can’t be expressed in Bitcoin transactions, the respective quantities are rounded right down to complete satoshis within the outputs of dedication transactions or when closing a channel. Any remaining break up satoshis are dropped to charges.