What Is Block Height?
Also known as: Block Number, Chain Height
In short
Block height is the sequence number of a block in the blockchain and shows the number of blocks added to the chain before that block. The height of the first block, the genesis block, is zero; the height of the latest block expresses the chain's current length.
Each new block takes a number one greater than the height of the previous block. Block height is used to locate a specific block and to define protocol events tied to timing. In Bitcoin, events such as the halving are tied to block height rather than date and occur every 210,000 blocks. For this reason, the date of the next halving is an estimate, but the block height at which it will occur is certain.
Block height is also used to calculate how many confirmations a transaction has received: the height of the block containing the transaction is subtracted from the chain's current height and one is added. For example, if the transaction is in block 100 and the chain's latest block is 105, the transaction has six confirmations. Time locks and soft fork activations can also be defined by a specific block height.
When a temporary fork occurs, more than one block can exist at the same height; in this case, the branch that accumulates more work or stake weight is considered valid, and the other block is left outside the chain. For this reason, the block's hash is used together with the height to identify a block definitively. The current block height can be tracked on block explorers.
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