A Bitcoin transaction is confirmed when it is combined in a block with other transactions and added to the blockchain. A new block is added approximately every 10 minutes, and every new block added thereafter means greater assurance of an irreversible transaction. For very large value transactions, six confirmations are generally desired, which can take an hour. For multi-million-dollar transactions, dozens of confirmations may be required. However, to buy an inexpensive item or send a small amount of coins to someone, very often no confirmation is needed.
Layer 2 Chains
To deal with confirmation delays, independent blockchains known as "sidechains" or "Layer 2 chains" are used to handle small transactions, each chain having no confirmation requirement or its own confirmation equivalency. After a certain number of transactions are added to these auxiliary chains, a summary is added to the main blockchain such as Bitcoin or Ethereum, which makes the transactions incontestable (see
sidechain and
Layer 2 blockchain). See
Bitcoin mining and
Bitcoin.