Jump to: , After a transaction is broadcast to the Bitcoin network, it may be included in a block that is published to the network.When that happens it is said that the transaction has been mined at a depth of 1 block.With each subsequent block that is found, the number of blocks deep is increased by one.To be secure against double spending, a transaction should not be considered as confirmed until it is a certain number of blocks deep.Contents 1 2 3 4 The classic bitcoin client will show a transaction as "n/unconfirmed" until the transaction is 6 blocks deep.Merchants and exchanges who accept bitcoins as payment can and should set their own threshold as to how many blocks are required until funds are considered confirmed.When potential loss due to double spending as nominal, as with very inexpensive or non-fungible items, people may choose not to wait for a transaction to be confirmed, and complete the exchange as soon as it is seen on the network.Most exchanges and other merchants who bear the risk from double spending require 6 or more blocks.

There is nothing special about the default, often-cited figure of 6 blocks.It was chosen based on the assumption that an attacker is unlikely to amass more than 10% of the hashrate, and that a negligible risk of less than 0.1% is acceptable.Both these figures are arbitrary, however; 6 blocks are overkill for casual attackers, and at the same time powerless against more dedicated attackers with much more than 10% hashrate.[1]Freshly-mined coins cannot be spent for 100 blocks.It is advisable to wait some additional time for a better chance that the transaction will be propagated by all nodes.Some older bitcoin clients won't show generated coins as confirmed until they are 120 blocks deep./~greg/attack_success.html) can be used to calculate the probability of a successful doublespend given a hashrate proportion and number of confirmations.Note that in the reality of bitcoin mining today, many more than 6 confirmations are required.(60 confirmations to have <1% odds of succeeding against an entity with 40% hash power) Each additional confirmation is a new block being found and added to the end of the blockchain.

Miners create blocks by solving the proof of work for their proposed block.The block interval has an average of 10 minutes but not every block interval is exactly 10 minutes.It follows a statistical process known as a poisson process, where random events happen with the same probability in each time interval.Another way of expressing this is that the mining process has no memory, at every second a block has the same chance of being found.Poisson processes are well-understood but can be unintuative.There are lots of block intervals with a time less than 10 minutes but then a few block intervals much longer which bump up the average to 10 minutes.So the bitcoin network can get unlucky and a block won't be found for a whole hour.In a 10 minute interval, the probability of a block being found is about 63% (or 1 - e^(-1)).So approximately two-thirds of the time a block will be found in 10 minutes or less.In 30 minutes a block has a 95% chance of being found, which rises to 99.7% if the time interval is 60 minutes.

Average confirmation times (self.Bitcoin)submitted by You all know this chart from Blockchain.info https://blockchain.info/charts/avg-confirmation-time.litecoin 1 gh/sBy the link name we would expect that it will show us average time transactions wait for first confirmation.ethereum studioBut it's actually a median time, and only considers transactions which have already confirmed, excluding transactions which may have been sitting in the mempool for hours.bitcoin dice source/ /spreadsheets/d/1aYfkjiN534p4zyE5WJNm7rddr84KS_e50EFTYJqj5jQ/edit#gid=1463201895 99.16% transactions which have 0.00005 BTC/Kb fees and higher have the average confirmation time of 43 minutes!bitcoin austin hillπ Rendered by PID 14269 on app-234 at 2017-06-24 12:30:46.214644+00:00 running 3522178 country code: SG.litecoin 3 year chart

The block size debate might seem unimportant to people who don't use bitcoin on a daily basis.However, the biggest challenge in bitcoin right now is dealing with confirmation time.bitcoin block confirmation timeThis is especially true during peak transaction periods.The problem starts when lots of transactions propagate the network.It is possible to use higher network fees on outgoing transactions for faster confirmation.However, this is not guaranteed.There are not many mobile wallets letting users change transaction fees.In addition, automated fee estimation usually doesn't work the way it should.Bitcoin users often have to wait more than 15 minutes for a transaction to confirm.Sometimes, transactions can even take up to four hours.Limited block sizes can even lead to a fee market for transactions.In theory, it is possible to automatically calculate an ideal miner fee.This would mean a transaction being confirmed in the first block.

Even so, the time a subsequent block is generated still is a random variable.It simply cannot be controlled.Here is an example of automated fee recommendation.By estimation, any transaction with a fee higher than 52,419 satoshis/KB would be included in the first block.Any transaction with fees lower than 25,000 satoshis/KB would need to wait at least two blocks to get confirmed.This is why it is interesting to do an experiment testing existing mobile bitcoin wallets.The goal: To see how they calculate fees.Also, how these wallets compete for transactions included in the first block.It should be noted during this test there were no bitcoin stress tests or transaction peaks occurring.So, the average time of one confirmation is around 23 minutes.This is a long time.There are 2.7 transactions broadcasted per second and 4,421 transactions in the mempool.This is quite low compared to the average number of transactions in mempool.The result of this experiment indicates transaction fees could help transactions get confirmed faster.

Even so, the fact no blocks could be generated for more than 40 minutes still causes issues.When the someone is trying to sell bitcoin for cash, there needs to be at least one confirmation.Also, none of these mobile wallets seem to choose mining fees efficiently depending on network state.They mostly rely on luck for fast confirmation.The bitcoin network block difficulty ensures the average time of a block in every 2,016 blocks is 600 seconds.As seen in the above chart, when block generation time (the confirmation time) decreases fast, there is a higher leap in block difficulty.Bitcoin adjusts difficulty every 2,016 blocks to keep up with the hashrate increase.The average block time is 10 minutes.In a perfect world, where the blocks are not full and all transactions have enough fees, every transaction should be included in the first block.This average is 10 minutes.As seen below, a median transaction confirmation with fees is around 8 minutes.However, it does not match our mobile wallet experiment.