What is block height?
In short
Block height is the number that shows a block’s position in the chain by counting how many blocks come before it. In Bitcoin, the first block has a height of 0.
Think of an apartment building that keeps adding new floors: the floor number tells you where it is, not what it contains. Block height works in much the same way. In Bitcoin, the very first block, known as the genesis block, is at height 0, the next one at 1, and the count keeps going.
Each new block links to the one before it and gets a height one higher. When we say the chain is at height 900,000, we mean its latest block has that number. Together with the genesis block at height 0, that chain contains 900,001 blocks.
Why it matters
If you’ve sent crypto, the height helps you understand where your transaction was recorded and how many confirmations it has gathered. In a block explorer you can find the block that contains it and compare it with the latest one.
For example, in Bitcoin, if a transaction went into block 100 and the chain has reached block 102, it has three confirmations: we count the block that contains it plus the next two. Confirmations aren’t the same number as the height.
Height is also used for events that activate at a specific block, such as Bitcoin’s halving. We find it useful to think of it as a reference point within the chain, not as a date on the calendar.
What to watch out for
The same height doesn’t necessarily mean the same block. During a temporary fork, there can be different candidate blocks at the same position. To pinpoint exactly which one you mean, you need its identifier, i.e. the hash.
Also, height isn’t a clock: blocks aren’t always produced at equal intervals. An estimate of when the network will reach a specific height can change. And comparing the heights of different blockchains doesn’t by itself show which network is faster or more secure.