Is it possible to calculate the transaction size from the transaction id ?

  • I think this should answer to your question more than exhaustively. If yes this can be marked as duplicate, I suppose.
    – AG23
    Commented Jan 15, 2019 at 11:05

1 Answer 1


No. That's not possible.

A transaction id is calculated from the raw transaction. More specifically the raw transaction is hashed twice with sha256: sha256(sha256(rawtransaction)).

That means, that the id is always 256 bits long (64 characters). Because sha256 and hashing in general is a one-way-operation, it's not possible to calculate the size of the rawtransaction just from the transaction id.

if you need more information about a transaction, you have to fetch that from a client. In bitcoin core you can use gettransaction or getrawtransaction. (getrawtransaction only works if the transaction belongs to one of your addresses or you have txindex enabled in your wallet.)

  • TXID is dsha256 +endian swap of the over-the-wire transaction serialisation.
    – James C.
    Commented Jan 15, 2019 at 10:28
  • That is part of the p2p protocol, not implementation, as this is how txids / prevouts are referenced in overthewire tx serialisations.
    – James C.
    Commented Jan 15, 2019 at 10:40

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