Block
A block is a batch of transactions the network adds to the blockchain in one go. It contains the hash of the previous block, so blocks form a chain that is hard to tamper with.
How it works
Transactions are not written to the blockchain one at a time. They first wait in the mempool, then a miner or validator packs them into a block and proposes it to the network. Once the network accepts the block, every transaction in it has its first confirmation.
A block has a header and a body. The header holds the previous block's hash, a timestamp, a fingerprint of all transactions and other technical data. The body holds the transactions. Change even one transaction in an old block and its hash changes, breaking the chain.
Networks produce blocks at different speeds: bitcoin about every 10 minutes on average, Ethereum every 12 seconds. Space in a block is limited, so when many people transact at once, fees rise and higher payers go first. A block's number in the chain is called its block height.
Bitcoin produces a block about every 10 minutes, so roughly 144 blocks per day (24 × 60 / 10). If an exchange waits for 3 confirmations, a deposit is credited in about 30 minutes on average, though a block can arrive after 1 minute or after 40.
A common mistake is believing a transaction is "on the blockchain" as soon as the wallet says "sent". Until it is in a block it may never land: with a low fee it can sit in the mempool for hours. Check the status in a block explorer and set the fee based on current network load.
Questions and answers
What is a block in a blockchain in simple terms?
It is one page of the network's shared ledger: a batch of transfers is written on it and bound to the previous page.
How often are new blocks created?
It depends on the network: about every 10 minutes on bitcoin, every 12 seconds on Ethereum, and faster on some others.
What is block height?
It is a block's position in the chain, counting from the very first (genesis) block. It is handy for finding blocks and counting confirmations.
Related terms
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Updated: 2026-10-19