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Block

A container of transaction data that is permanently recorded on a blockchain.

A block is a fundamental unit of a blockchain — a data structure that contains a batch of validated transactions. Blocks are linked together chronologically using cryptographic hashes, forming the "chain" in blockchain.

What's Inside a Block

Block Header: Contains metadata including the previous block's hash, a timestamp, the Merkle root of all transactions, the nonce (for PoW chains), and the difficulty target.

Transaction Data: The list of validated transactions included in the block.

Block Hash: A unique cryptographic fingerprint of the block, derived from the header data.

Block Size

Different blockchains have different block size limits. Bitcoin's block size is limited to approximately 1-4 MB (with SegWit), while other chains allow larger blocks for higher throughput. Block size is a key factor in a network's scalability — the Bitcoin block size debate led to the Bitcoin Cash fork in 2017.

Block Time

Block time is the average interval between new blocks. Bitcoin targets 10 minutes, Ethereum approximately 12 seconds, and Solana about 400 milliseconds.

Frequently Asked Questions

What is a block in blockchain?

A block is a container of transaction data that is permanently recorded on a blockchain. Each block contains a batch of validated transactions, a timestamp, and a cryptographic link to the previous block, forming a chain.

How big is a Bitcoin block?

Bitcoin blocks have a limit of approximately 1-4 MB (with SegWit). Each block is mined approximately every 10 minutes and can contain several thousand transactions.

What determines block time?

Block time is set by the protocol's design and maintained through difficulty adjustments. Bitcoin targets 10 minutes, Ethereum about 12 seconds, and Solana about 400 milliseconds.

Related Terms

Blockchain

A distributed digital ledger that records transactions across a network of computers.

Block Explorer

A web tool for searching and viewing blockchain transactions, addresses, and blocks.

Block Height

The sequential number of a block in the blockchain, counting from the genesis block.

Block Reward

The cryptocurrency awarded to miners or validators for successfully adding a new block.

Difficulty

A measure of how hard it is to mine a new block on a proof-of-work blockchain.

Genesis Block

The very first block ever mined on a blockchain network.

Hash Function

A mathematical function that converts input data into a fixed-size string of characters.

Immutable

A property of blockchain data meaning it cannot be changed or deleted once recorded.

Mining

The process of validating transactions and creating new blocks using computational power.

Node

A computer connected to a blockchain network that validates and relays transactions.

Nonce

A number used once in cryptographic operations, critical for mining and transaction ordering.

Transaction Fee

A fee paid to miners or validators for processing a blockchain transaction.

UTXO

Unspent Transaction Output — the remaining cryptocurrency after a transaction.