I think I understand mining well enough, but what I don't get is how the blocks of transactions are assembled. According to this post - What exactly is Mining? - the miners assemble the blocks and then solve for the difficulty.

So, once a block is solved and the miners need to create a new block, how do the miners decide how many transactions to put in the block? Could the miner just assemble a block with a single transaction? Could certain blocks contain more or less transactions than another? Thanks!

2 Answers 2


Technically a block with just one transaction in it would be valid. However miners have an incentive to add more transactions to the block they are currently mining because they receive the transaction fees attached to those transactions.

  • another question... could miners ignore transactions that didn't pay fees?
    – a432511
    Commented May 12, 2014 at 15:03
  • Yes; and they are actively doing that as well. Giving priority to higher fees and omitting none/lower fees.
    – Maran
    Commented May 12, 2014 at 15:14

could miners ignore transactions that didn't pay fees?

yes. bitcoin is voluntary system. each miner has a right to include or skip any transaction.

(not asked questions)

why do miners include free transactions?

Why not? The system is for people, not people for system.

do miners include all free transactions?

No! There are some recommended rules https://en.bitcoin.it/wiki/Transaction_Fee

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