A txid is the double SHA-256 hash of a transaction, shown in reverse byte order. Learn how it is made, where to find it and how to look one up.
A fingerprint of the transaction
A transaction ID is created by hashing the transaction's data twice with SHA-256. Change one byte and the txid changes completely.
Why reversed?
Internally Bitcoin treats the hash as a little-endian number. Explorers and wallets show it reversed so it reads like a normal big-endian number. See Bytes and endianness. If you hash a raw transaction yourself, remember to reverse the result.
txid vs wtxid
- txid hashes the transaction without Witness data. Because signatures are left out, a third party can't change the txid by tweaking a signature (a problem called malleability, fixed by Segregated Witness (SegWit)).
- wtxid includes the witness. It is used inside blocks to commit to witness data.
A famous txid
The genesis block's only transaction has txid 4a5e1e4baab89f3a32518a88c31bc87f618f76673e2cc77ab2127b7afdeda33b. It is also the Merkle trees and the merkle root of block 0, because a block with one transaction has that transaction's hash as its root.
Where to find your txid
- In your wallet: open the payment's details; look for "transaction ID", "txid" or "hash".
- From an exchange: withdrawal history usually links the txid.
- On MyBitcoinExplorer: paste it into the search to see status, fee and confirmations.
Why the txid can change before confirmation
If a payment is replaced with RBF to raise its fee, the new version is a different transaction with a new txid. The old txid will never confirm. Always check the latest txid your wallet shows.
Key takeaways
- A txid is the double SHA-256 of the transaction without witness data.
- It's displayed in reversed byte order.
- Excluding the witness makes txids immune to signature malleability.
Common questions
Can two transactions have the same txid?
In practice no. Finding two different transactions with the same SHA-256 hash is considered infeasible.
Why can't I find my txid in an explorer?
It may not have reached that node yet, may have been replaced, or the explorer may need a transaction index for old transactions.
Is a txid secret?
No. It's public and safe to share. It reveals the transaction, which is already public.
Is the txid the same as a transaction hash?
Usually yes. Some tools also show the wtxid, which includes witness data.