Blockchain Confirmations Definition

| Publish date: 01/19/2018 (Last updated: March 07, 2018 09:04 AM)

What are Blockchain Confirmations?

Blockchain Confirmations are additional blocks that are added to the blockchain after the transaction in question. The transaction that is mined is part of “block one”; each subsequent block is a confirmation. Confirmations are important to cryptocurrency users because they help minimize double-spend risk and ensure transaction validity.

Entities who accept cryptocurrency transactions like exchanges and merchants should establish their own thresholds for what constitutes a confirmed transaction. This will ensure that the payment they’ve just received is legitimate.

The number of confirmations

The default depth is six blocks for the Bitcoin network, though this is largely arbitrary. Likewise, it is suggested that Ethereum users wait twelve confirmations. However, there is no set rule that determines how many blocks are required; some choose not to wait for a transaction to be confirmed and simply complete the transaction once it appears on the network.

For larger transactions with the irreversible sale of items or services, it is recommended that the confirmation depth is increased. Depending on the nature of the transaction, it is not uncommon for confirmation times to last one full day.

Here is a table detailing how long it would take to see ten blocks confirmed for four different cryptocurrencies:

Block Time (min)
# of Blocks
# of Minutes Total

As the table shows, the time it takes to reach a target level of confirmations is directly related to the cryptocurrency’s block time. The longer it takes to mine a block, the longer it takes to reach a confirmation threshold.

Confirmations Prevent Double Spending

The cryptocurrency double-spending problem is the risk that the same cryptocoin will be spent using multiple transactions. The use of a blockchain mitigates this risk by creating a timestamped ledger where all transactions are kept.

0/unconfirmed transactions are pretty common for merchant payments. However, they aren’t very safe as they can be easily double-spent, meaning a vendor loses money.

Satoshi Nakamoto

In order to be sure that double spending hasn’t taken place and that the transaction is irreversible, it shouldn’t be considered as confirmed until a certain amount of blocks have been processed. When the given transaction is mined within a block, it is considered to have been mined at one block deep. Each subsequent block mined after the initial block increases the block depth by one.


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