Overview
Block height is a simple sequential counter that identifies each block's position in the blockchain. The genesis block has height 0, the next block has height 1, and so on. Block height serves as a universal reference system for identifying when events occurred in Bitcoin's history.
How Block Height Works
Height 0: [Genesis Block]
│
Height 1: [Block 1]
│
Height 2: [Block 2]
│
... │
│
Height N: [Current Tip]
Each block's height is exactly one greater than its parent's height. Since blocks are produced approximately every 10 minutes, the block height also provides a rough indicator of time elapsed since Bitcoin's launch.
Notable Block Heights
- 0: Genesis block, mined January 3, 2009
- 210,000: First halving (reward dropped from 50 to 25 BTC)
- 420,000: Second halving (25 to 12.5 BTC)
- 630,000: Third halving (12.5 to 6.25 BTC)
- 840,000: Fourth halving (6.25 to 3.125 BTC)
Block Height vs Block Hash
While block height is a convenient reference, it is not always unique during temporary chain splits (two blocks can briefly share the same height on different forks). The block hash is always unique and provides an unambiguous identifier. In practice, once a block is buried under several confirmations, its height is effectively unique in the canonical chain.
Usage in Protocol Rules
Block height is used in several consensus rules, including the halving schedule (every 210,000 blocks), difficulty adjustments (every 2,016 blocks), and certain timelock conditions that specify a minimum block height before a transaction can be confirmed.