The security parameter k is set to 2160 blocks. The code comment describing this genesis parameter makes it crystal clear it defines the maximum number of blocks the chain could potentially roll back. 2160 blocks equals 43,200 slots, or 12 hours.


The Ouroboros security parameters, aka k. This is the maximum number of blocks the node would ever be prepared to roll back by.

Clients of the node following the chain should be prepared to handle the node switching forks up to this long.

Source: https://github.com/input-output-hk/cardano-node/blob/master/cardano-api/src/Cardano/Api/GenesisParameters.hs#L55-L61

and the description in CIP#9

After how many blocks is the blockchain considered to be final, and thus can no longer be rolled back (i.e. what is the maximum allowable length of any chain fork).

Source: https://cips.cardano.org/cips/cip9/

to this article in the official docs

A transaction becomes immutable as soon as its depth is greater than 3k/f slots (that is, 129600 slots on current mainnet, or 36 hours).

Source: https://docs.cardano.org/learn/chain-confirmation-versus-transaction-confirmation

Can someone please explain

  • what is the source for the docs to come up with this formula 3k/f?
  • which statement is correct (12h or 36h), and why?

1 Answer 1


The documentation site (docs.cardano.org) is wrong, the one in genesis is correct.

Unfortunately I find it painful that ones maintaining/merging documents are not hands on - so depend on others to provide correctness of data. Hopefully you can address it via PR

  • Thanks for the answer. I do believe you, but can you also explain why the supposedly wrong docs came up with this formula in the first place? I mean who would just make up a formula from thin air.
    – LACE pool
    Aug 29, 2022 at 21:44
  • I can see this false statements were already brought in with the first commit github.com/input-output-hk/cardano-documentation/commit/… I can also see you've submitted some changes to the file yourself. I presume you didn't know either at the time.
    – LACE pool
    Aug 29, 2022 at 22:08
  • I asked them to correct it before (earlier version they confused k with nOpt), the updated version is no better either, as it uses false statements. In the end , problem remains the ones maintaining docs want to go back to their IO team for confirmations and come back with half corrections, I gave up on the mentioned site, better for community to focus on preparing documentations on developers.cardano.org instead of 1 org vertical structure
    – RdLrT
    Aug 30, 2022 at 4:20

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