<p>I assume that James is using &quot;sat/kw&quot;, to refer to &quot;satoshi per kiloweightunit&quot; as a means to express the fee rate of a transaction. &quot;Weight&quot; here refers to what replaced &quot;blocksize&quot; as a blockspace limit in the protocol rules with the segwit softfork.</p>
<p>I'm seeing &quot;sat/kw&quot; for the first time in this context. I've seen <code>wu</code> used before to refer to weightunits instead of <code>w</code>, but the related unit &quot;virtual bytes <code>vB</code>&quot; seems to be more common in the context of feerates generally.</p>
<p>I've explained the relationship of blocksize, virtual size, and weight in depth here: <a href="https://bitcoin.stackexchange.com/q/89385/5406">Is there a difference between bytes and virtual bytes (vbytes)?</a></p>

CC BY-SA 4.0
2019-08-12T08:09:46.720Z
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
CC BY-SA 4.0
2019-08-11T18:35:13.527Z
2024-01-31T13:50:17.490Z
2024-01-31T13:50:17.490Z
Murch
<p>Whilst learning about bitcoin &amp; lightning fees I have encountered the abbreviation sat/kw a few times, most recently here:</p>

<p><a href="https://bitcoin.stackexchange.com/questions/83135/why-can-t-lightning-tx-s-be-signed-with-sighash-single-to-allow-for-fee-updates?r=SearchResults&amp;s=1|46.6782">Why can’t lightning tx’s be signed with sighash single to allow for fee updates?</a></p>

<p>Is it a ratio of satoshis per kilowatt?</p>

<transaction-fees><terminology><block-weight>
what is measured in units of sat/kw?
thermalCat
# what is measured in units of sat/kw?

(Asked by: username_0 on 2019-08-11)

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?](https://bitcoin.stackexchange.com/questions/83135/why-can-t-lightning-tx-s-be-signed-with-sighash-single-to-allow-for-fee-updates?r=SearchResults&s=1|46.6782)

Is it a ratio of satoshis per kilowatt?

**Tags:** transaction-fees, terminology, block-weight


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## 1 answers

### Answer by username_1 on 2019-08-11. Score: 7 | Accepted answer

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`, but the related unit "virtual bytes `vB`" seems to be more common in the context of feerates 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)?](https://bitcoin.stackexchange.com/q/89385/5406)

> **Comments:**
> **username_2**: Actually in the BOLTs, kw is used to calculate fees for commitment transactions. So I think Jannes picked up "sat/kw" from there.  

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