Definition
A block confirmation is a metric that shows how many additional blocks have been added to the blockchain after the block containing a given transaction. It is used as an indicator of how securely a transaction is embedded in the chain. When a transaction is first included in a block, it has one confirmation, and each new block added on top of that block increases the confirmation count by one. This growing number reflects the increasing difficulty of reversing or altering that transaction through a reorg of the chain.
Block confirmations are closely tied to concepts like block height and finality. The block height identifies the position of a block in the chain, and confirmations measure how far that block is from the current tip of the chain. Higher confirmation counts generally correspond to stronger economic and probabilistic guarantees that the transaction will not be removed or replaced. Different applications and services may require a specific number of confirmations before treating a transaction as effectively final.
Context and Usage
In practice, block confirmations provide a simple way to express the security depth of a transaction within the blockchain. Because new blocks extend the chain, each additional block makes a past block more resistant to being reorganized. A low confirmation count means a transaction is relatively recent and more exposed to potential changes from a reorg. A high confirmation count signals that the transaction is deeply embedded and approaching the level of finality expected by most users and services.
This metric is typically displayed alongside each transaction and block in blockchain explorers and related tools. It helps users, applications, and infrastructure providers decide when to treat a transaction as settled according to their own risk tolerance. While confirmations do not guarantee absolute finality in all blockchain designs, they are a widely used proxy for the security and permanence of a transaction’s inclusion in a specific block.