Block Height
Last reviewed: December 18, 2025
Block height is the sequential number of a block in the blockchain, representing how many blocks exist between it and the genesis block (the first block, which has height 0), essentially measuring the blockchain's length.
Detailed Explanation
Common Questions
Use a blockchain explorer like Blockchain.com for Bitcoin or Etherscan for Ethereum. Enter your transaction ID (hash), and the explorer displays the block height containing your transaction. For example, if your transaction is in Bitcoin block 800,500, that's your transaction's block height. To calculate confirmations, subtract your block height from the current block height shown on the explorer's homepage. If the current height is 800,506, you have six confirmations (800,506 - 800,500 = 6). Most explorers display confirmation count automatically, but understanding the block height calculation helps you verify this information independently and understand what confirmations actually mean - they're literally the number of blocks built on top of yours.
Block height depends on blockchain age and block creation speed. Bitcoin launched in 2009 and creates blocks every 10 minutes, giving it over 800,000 blocks. Ethereum launched in 2015 with 12-15 second blocks, resulting in millions of blocks despite being younger. A blockchain that creates blocks twice as fast will have twice the height over the same time period. Block height doesn't indicate superiority - it's just a measurement reflecting the blockchain's history and design. What matters is the blockchain's security, adoption, and utility, not height. When comparing blockchains, consider factors like hash rate security, transaction volume, and economic activity rather than block height. Height is useful for referencing specific blocks within a single blockchain, not for cross-blockchain comparisons.
During a blockchain fork, competing chains temporarily exist at the same height until one grows longer. When two miners find valid blocks simultaneously, both blocks might be at height 800,000, creating two competing chains. Miners seeing the first block build on it, while others build on the second, creating heights 800,001a and 800,001b. The network resolves this by following the longest chain rule - whichever chain reaches height 800,002 first becomes the accepted chain, and the other chain's blocks become orphaned. For hard forks creating new cryptocurrencies (like Bitcoin Cash from Bitcoin), both chains share history up to the fork height, then diverge permanently into independent chains with separate height counting. Understanding this helps you grasp why multiple confirmations provide security - your block height might temporarily be on the losing fork.
Common Misconceptions
Block height only measures blockchain length, not quality or security. A blockchain creating blocks every second will have higher height than one creating blocks every 10 minutes, but that doesn't make it superior. Security comes from the economic cost of attacking the chain (hash rate for PoW, stake for PoS), not block count. Bitcoin's relatively modest height compared to some newer blockchains doesn't mean it's less secure - actually, Bitcoin's enormous hash rate makes it the most secure blockchain despite slower block times and lower height growth. When evaluating blockchains, consider security mechanisms, adoption, and economic activity rather than block height. Height is useful for referencing specific blocks within a blockchain, not for comparing blockchain quality across different protocols.
Block height and block hash are completely different identifiers. Block height is the sequential position number (like 'book 5 in the series'), while block hash is the unique cryptographic identifier (like a book's ISBN number). Every block has both: a height indicating its position in the chain and a hash uniquely identifying it. You can reference blocks using either system - 'Bitcoin block 500,000' uses height, while '0000000000000000007962066dcd6675830883516bcf40047d42740a85eb2919' is that same block's hash. Height is easier for humans to remember and use, while hashes are necessary for cryptographic verification and linking blocks together. Understanding this distinction helps you use blockchain explorers effectively and communicate clearly about specific blocks.
Temporarily, multiple blocks can exist at the same height during natural blockchain operation. When two miners find valid blocks almost simultaneously, both blocks might be at height 800,000, creating competing chains. Different network participants might see different blocks first, temporarily disagreeing on which block 800,000 is valid. The network resolves this within one or two blocks when one chain grows longer - the longest chain wins, and the orphaned block's height becomes unused in that chain's history. This is normal and happens regularly. After multiple confirmations, having competing blocks at the same height becomes increasingly improbable. This temporary height ambiguity is exactly why waiting for multiple confirmations matters - you want to ensure your block height is on the permanent chain, not a temporary fork that will be orphaned.