<p>There is nothing particularly special about six. Five blocks would take less time but provide a slightly lower level of assurance. Seven blocks would take longer but would provide a slightly higher level of assurance. Lots of services use fewer than six blocks.</p>

CC BY-SA 3.0
2017-12-28T00:18:52.410Z
2017-12-28T00:18:52.410Z
David Schwartz
<p>in addition to @David answer read more about <a href="https://en.bitcoin.it/wiki/Irreversible_Transactions" rel="nofollow noreferrer">Irreversible Transactions</a></p>

<hr>

<blockquote>
  <p>For example, if the attacker controls 10% of the network hashrate but
  the merchant waits for 6 confirmations, the success probability is on
  the order of 0.1%[3]. Because of the opportunity cost of this attack,
  it is only game-theory possible if the bitcoin amount traded is
  comparable to the block reward (but note that an attacking miner can
  attempt a brute force attack against several counterparties at once).</p>
</blockquote>

CC BY-SA 3.0
2017-12-28T01:49:43.647Z
I'm not understnading how the irrevisibliyt of transactions in any way explains why "six" became some sort of unspoken standard.  @David's answer suggests that there is indeed nothing special about 6.
Dave
CC BY-SA 3.0
2017-12-28T07:49:41.727Z
six became a good value, cause after one hour (each block 10min) you had to have so much hash power, that it seems impossible, that someone could re-create the blockchain and make your tx pa to someone else. So as David said, nothing really special, just good sanity and caution for higher values.
pebwindkraft
CC BY-SA 3.0
2017-12-28T11:05:18.620Z
I've edited the answer!  @Dave
Tailer
CC BY-SA 3.0
2017-12-28T00:55:34.333Z
2017-12-28T11:04:47.473Z
2017-12-28T11:04:47.473Z
Tailer
<p>I read that when your transaction is part of a block that has five other blocks on top of it, you can feel safe that your transaction is not in danger of being orphaned because someone else would come along and confirm a series of blocks longer than the one of which your transaction belongs. My question is what's so special about six?  It seems like an arbitrary number. Why not five or seven?</p>

CC BY-SA 3.0
2017-12-28T08:49:52.187Z
Possible duplicate of [Why is 6 the number of confirms that is considered secure?](https://bitcoin.stackexchange.com/q/1170/5406)
Murch
<transactions><blockchain><unconfirmed-transactions><proof-of-work><block>
What's so special about six blocks for confirming transactions?
Dave
# What's so special about six blocks for confirming transactions?

(Asked by: username_0 on 2017-12-28)

I read that when your transaction is part of a block that has five other blocks on top of it, you can feel safe that your transaction is not in danger of being orphaned because someone else would come along and confirm a series of blocks longer than the one of which your transaction belongs. My question is what's so special about six? It seems like an arbitrary number. Why not five or seven?

**Tags:** transactions, blockchain, unconfirmed-transactions, proof-of-work, block

> **Comments:**
> **username_1**: Possible duplicate of [Why is 6 the number of confirms that is considered secure?](https://bitcoin.stackexchange.com/q/1170/5406)  

---

## 2 answers

### Answer by username_2 on 2017-12-28. Score: 2 | Accepted answer

There is nothing particularly special about six. Five blocks would take less time but provide a slightly lower level of assurance. Seven blocks would take longer but would provide a slightly higher level of assurance. Lots of services use fewer than six blocks.


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### Answer by username_3 on 2017-12-28. Score: 0

in addition to @David answer read more about [Irreversible Transactions](https://en.bitcoin.it/wiki/Irreversible_Transactions)

---

> For example, if the attacker controls 10% of the network hashrate but
> the merchant waits for 6 confirmations, the success probability is on
> the order of 0.1%[3]. Because of the opportunity cost of this attack,
> it is only game-theory possible if the bitcoin amount traded is
> comparable to the block reward (but note that an attacking miner can
> attempt a brute force attack against several counterparties at once).

> **Comments:**
> **username_0**: I'm not understnading how the irrevisibliyt of transactions in any way explains why "six" became some sort of unspoken standard.  @David's answer suggests that there is indeed nothing special about 6.  
> **username_4**: six became a good value, cause after one hour (each block 10min) you had to have so much hash power, that it seems impossible, that someone could re-create the blockchain and make your tx pa to someone else. So as David said, nothing really special, just good sanity and caution for higher values.  
> **username_3**: I've edited the answer!  @username_0  

---

