While looking in mempool i saw with increase in sat/vbyte the number of transactions decrease. are they somehow related?

  • Hi sat crazy, could you clarify what data you are looking at for your observation? The title makes me think that you are looking at past blocks and see that higher feerates correlate with fewer transactions, but the body of your post makes me think that you are looking at a mempool visualizer.
    – Murch
    Dec 1 '21 at 18:41

The way I interpret your question, you were looking at a mempool visualizer like the following: enter image description here

And you are asking why there are strictly fewer transactions for every fee rate band with higher feerates.

Most of these mempool visualizations don't give the count of transactions in each band, but the count of all transactions in the feerate band and above. If you carefully inspect the legend, you see that e.g. the highlighted row says "8+: 6,811 tx" and not "8-10: 6,811 tx". The row's number includes all transactions that pay at least 8 sat/vB.


The number of transactions in a (full) block depends on the average transaction size, which in turn depends on the number of inputs and outputs of a transaction (and also on the specific output types used). There are several main types of large transactions:

  • Batched payment – one transaction paying multiple participants at once. Used extensively by exchanges to save on fees. (example)
  • Consolidation – a user consolidating their many unspent outputs into one to save on future fees. (example)
  • CoinJoin – many users mixing coins within a transaction in a way that breaks chain analysis heurestics. (example)

I don't think any of these occur more frequently during times of higher fees, and it's reasonable to assume consolidations will be happening when fees are low. So if there is any relationship between fee rate and number of transactions in a block, my guess is that it's actually the opposite of what you've observed.

  • why is it then that some blocks get filled with less number of transactions (i mean <1MB) even when there are many transactions in the mempool.
    – sat crazy
    Dec 1 '21 at 11:40
  • 1
    @satcrazy I've never seen a block with unused space when there were enough transactions in the mempool to fill it (excluding empty blocks which is a different matter entirely). Dec 1 '21 at 12:42

why does the number of transactions per block reduces with increase in transaction fees? While looking in mempool i saw with increase in sat/vbyte the number of transactions decrease. are they somehow related?

I am assuming you are trying to compare fee rate and transactions per block. I have shared the charts comparing both since 2016.

There are only 3 major spikes in fee rate chart and I don't see transactions per block reducing in that period when fee rates increased. There could be some correlation with BTCUSD price or other things but its unrelated to question.

First chart: BTC/MB Second Chart: Tx/Block


Date Tx/Block Range BTC/MB Range
Dec 2017 2100 - 2400 (10% segwit) 4 - 10
May 2019 ~2400 (30% segwit) 0.9 - 1.7
Apr 2021 ~2000 (50% segwit) 0.7 - 2.5

29 November 2021:

Tx/Block BTC/MB
2345 (80% segwit) 0.05

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