As for calculating time, I think that in normal times, as for times of congestion on the network, this number is not correct at all. Sometimes it took me more than 24 hours to get one confirmation.They are estimated numbers and likely averaged numbers for normal conditions, not for times when network is attacked or congested.
It is also known that the security of a Bitcoin transaction requires 6 confirmations for the transaction to be accepted, but my question is why do some exchanges suffice with only one confirmation and others 3?They can accept a deposit transaction after 1 or 3 confirmations, it depends on each exchange.
I tried a lot of exchanges that accept transactions after only 3 confirmations.
If you are patient enough to wait for at least one confirmation then you are no longer vulnerable to race attacks or Finney attacks. Now your only concern is 51% attacks. What's the rule of thumb for an acceptable number of confirmations?
- 1 confirmation: sufficient for small payments less than $1,000.
- 3 confirmations: for payments $1,000 - $10,000. Most exchanges require 3 confirmations for deposits.
- 6 confirmations: good for large payments between $10,000 - $1,000,000. Six is standard for most transactions to be considered secure.
- 10 confirmations: suggested for large payments greater than $1,000,000.