What is block height?

The number of blocks between a given block and the genesis block, used as the chain's clock.

Heights are how protocol events are scheduled, since block counts are objective while wall-clock time is not: Bitcoin's halvings fire at fixed heights rather than fixed dates (source: Bitcoin developer documentation). Exchanges express deposit requirements in blocks for the same reason, crediting funds after a set number of blocks have been built on top of the one holding your transaction.

Height is not a timestamp. The average block interval is a target, not a guarantee, which is why events scheduled by height drift by days against the calendar.

How it works

The genesis block is height 0. Every subsequent block increments by one, so the height of the newest block is also the count of blocks that have ever been produced on that chain.

Because the count is derived from the chain itself rather than from any clock, every node agrees on it without needing synchronized time. Block timestamps exist but are loosely constrained and can be manipulated within limits, which is why consensus rules that need a schedule use height instead.

Protocol changes activate at heights. Bitcoin's halvings occur every 210,000 blocks, and soft fork activations have historically been specified by height or by signaling measured over height windows.

Heights near the tip are provisional. A chain reorganization can replace the most recent blocks, so a transaction confirmed at a given height can end up at a different one, or back in the mempool. Depth below the tip is what makes that unlikely.

Comparing your node's height against a public explorer's is the fastest way to tell whether a wallet is still syncing or is actually up to date.

Example

Illustrative: your transaction is included at height 870,000 and the network tip is 870,004. That is five confirmations, counting the block containing it. An exchange requiring six confirmations credits you once the tip reaches 870,005. If a reorganization replaces the last two blocks, your transaction may return to the mempool and confirm again at a different height, which is why the requirement exists.

Why it matters when you buy

Deposit and withdrawal waits are counted in blocks, not minutes, so the same confirmation requirement means very different waits on different chains. Knowing the current height and your transaction's height tells you exactly how long remains, rather than guessing from a progress bar. See the guide on using a block explorer.

Related terms

• block — what the count is counting
• confirmation — depth measured in blocks below the tip
• genesis block — height 0, where the count starts
• chain reorganization — why recent heights are provisional
• bitcoin halving — an event scheduled by height
• block explorer — where you check the current height

Questions

Is block height the same as a timestamp?

No. Height counts blocks and is objective; timestamps are set by the producer within loose bounds. Events that must be unambiguous are scheduled by height.

Why do halving countdowns keep changing?

Because they convert a fixed block height into a date using recent block pace. When blocks come faster or slower than the ten-minute target, the estimated date moves.

What does it mean when two explorers show different heights?

Usually that one is momentarily behind, which resolves in seconds. A persistent difference can indicate a chain split, which is rare and would be widely reported.