<p>A transaction ID is a 256 bit hash of transaction header data, so it is a 256 bit integer number. There can only be two to the power 256 distinct numbers that can be stored in 256 bits.</p>
<p>Bitcoin now has a rule that Transaction IDs must not be duplicated in the Blockchain <em>unless the previous instances of that txid have had all of their outputs spent</em>.</p>
<p>If all hashes are used and present in the Blockchain <em>with at least one unspent output</em>, there can be no more transactions under current rules.</p>
<p>However, 2<sup>256</sup> is a large number. it is quite close to the number of atoms in the universe.</p>

CC BY-SA 4.0
2024-02-10T19:31:11.557Z
txids can be duplicated as long as the previous instance of that txid has had all of its outputs spent.
Ava Chow
CC BY-SA 4.0
2024-02-10T22:24:29.537Z
@AvaChow: Thanks for the correction, answer updated
RedGrittyBrick
CC BY-SA 4.0
2024-02-10T18:55:49.790Z
2024-02-10T22:24:13.323Z
2024-02-10T22:24:13.323Z
RedGrittyBrick
<p>I know that there are an upper limit to the number of hashes that can be mined. But I do not know why is this a case? I guess it is due to the enormous amount of computation necessary to find hashes. Or is it due to some mathematical law?</p>
<p>In any case, my question would be what happens if all of hashes are used in the blockchain? Can we continue make new transactions?</p>

<transactions><blockchain>
What happens if all transactions are being used?
Péter Szilvási
# What happens if all transactions are being used?

(Asked by: username_0 on 2024-02-10)

I know that there are an upper limit to the number of hashes that can be mined. But I do not know why is this a case? I guess it is due to the enormous amount of computation necessary to find hashes. Or is it due to some mathematical law?

In any case, my question would be what happens if all of hashes are used in the blockchain? Can we continue make new transactions?

**Tags:** transactions, blockchain


---

## 1 answers

### Answer by username_1 on 2024-02-10. Score: 4 | Accepted answer

A transaction ID is a 256 bit hash of transaction header data, so it is a 256 bit integer number. There can only be two to the power 256 distinct numbers that can be stored in 256 bits.

Bitcoin now has a rule that Transaction IDs must not be duplicated in the Blockchain *unless the previous instances of that txid have had all of their outputs spent*.

If all hashes are used and present in the Blockchain *with at least one unspent output*, there can be no more transactions under current rules.

However, 2256 is a large number. it is quite close to the number of atoms in the universe.

> **Comments:**
> **username_2**: txids can be duplicated as long as the previous instance of that txid has had all of its outputs spent.  
> **username_1**: @username_2: Thanks for the correction, answer updated  

---

