What is block height?

Block height identifies a block’s position in a blockchain. In Bitcoin, the first, or genesis, block has height 0. Subsequent blocks have heights 1, 2, 3 and so on, increasing by one per block.

A block is a batch of transactions and related data. Height locates these records and commonly helps calculate confirmations or determine when a rule takes effect.

What is block height used for?

A block explorer queries on-chain blocks and transactions. A transaction lookup usually shows its block height. Comparing it with the latest height shows how many blocks have followed.

Height can also trigger protocol rules. Bitcoin reduces the new-coin subsidy every 210,000 blocks: Bitcoin halving. The rule follows block position, not a calendar date.

Some upgrades or transaction-validity conditions also use height. Protocols define the details; not every condition depends only on height.

How do you calculate confirmations?

In Bitcoin, the block including a transaction on the currently adopted chain counts as its first confirmation. Each subsequent block adds one.

As long as that block remains on the current chain:

Confirmations = latest block height − transaction block height + 1

For example, inclusion at 800,000 and latest height 800,005 means five later blocks plus the inclusion block: 800,005 − 800,000 + 1 = 6. The numbers are illustrative.

More confirmations mean more accumulated blocks after the transaction. Recipients choose how many to wait for by use case; this is not a guarantee that nothing can change.

What should you watch for?

Different blocks can share a height. Two miners can propose blocks at similar times, creating competing branches. The same height can have different contents. Identify the network and block hash—a rule-calculated block identifier—to specify a particular block.

Confirmations depend on the currently adopted chain. A node running validation software switching to another valid branch is a chain reorganization. A transaction from the old branch may leave the current chain; subtracting its old height no longer calculates confirmations.

Height is not directly convertible to a date. Bitcoin targets roughly ten-minute average block intervals, but individual intervals vary. Reaching a future height can only be estimated.

Networks can differ in block speed and numbering. Higher height alone does not prove longer operation, greater safety or more activity.

Related terms

Explore blocks, blockchain and Bitcoin halving, or return to the crypto glossary.

References

• Bitcoin developer documentation: Blockchain and height