Whilst learning about bitcoin & lightning fees I have encountered the abbreviation sat/kw a few times, most recently here:

Why can’t lightning tx’s be signed with sighash single to allow for fee updates?

Is it a ratio of satoshis per kilowatt?


I assume that James is using "sat/kw", to refer to "satoshi per kiloweightunit" as a means to express the fee rate of a transaction. "Weight" here refers to what replaced "blocksize" as a blockspace limit in the protocol rules with the segwit softfork.

I'm seeing "sat/kw" for the first time in this context. I've seen wu used before to refer to weightunits instead of w, and "virtual bytes vB" seem to be more common generally.

I've explained the relationship of blocksize, virtual size and weight in depth here: Is there a difference between bytes and virtual bytes (vbytes)?

  • 1
    Actually in the BOLTs, kw is used to calculate fees for commitment transactions. So I think Jannes picked up "sat/kw" from there.
    – Ugam Kamat
    Aug 12 '19 at 8:09

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