Block Height
What Is Block Height?
Block height is the number of blocks confirmed in a
blockchain network, counted from the very first block to the most recent one. The first block, known as the
genesis block, has a block height of 0. The block mined right after it has a height of 1, and the count continues to rise as new blocks are added.
Apart from the genesis block, every block contains a reference (a hash) to the block immediately before it. This linking is what gives each block its position, or height, in the sequence. Because the blocks are connected in order, block height provides a simple way to identify exactly where a block sits in the chain.
How Block Height Works
A useful way to picture a blockchain is as a stack of building blocks. You cannot pull a block out of the middle without disturbing everything stacked above it. Each new block is added on top, and the block height reflects how many blocks have been mined or validated since the network launched. Many of these blocks also carry a
block reward for the participant that added them.
In broad terms, you can estimate block height by dividing the time since the network launched by its average block time. The average block time tends to stay close to a target value, which the network maintains by adjusting its
mining difficulty. As the total
hash rate of the network changes, the difficulty adjusts so that blocks continue to appear at a fairly steady pace. For Bitcoin, the target block time is around 10 minutes on average.
Why Block Height Matters
Block height should not be compared directly across different blockchains, since each network can have a different average block time and a different hash rate. A height of one million on one chain does not represent the same amount of elapsed time as the same height on another.
Block height is also helpful for checking whether a copy of a blockchain is up to date. A local copy held by a
node may be considered out of sync if its block height differs from the height accepted across the wider network. Comparing the two values is a quick way to confirm whether the local copy reflects the latest state of the chain.