Block
15/04/2026
A block is a data structure that contains a batch of validated transactions and is permanently added to a blockchain. Each block links to the previous one, forming an unbroken chain of transaction history going back to the very first block — the genesis block.
What's inside a block?
Every block contains:
- Transaction data — a list of all transfers included in this block
- Block header — metadata including timestamp, difficulty target, and the hash of the previous block
- Nonce — a random number miners adjust when searching for a valid hash
- Merkle root — a compact fingerprint of all transactions in the block
How miners create blocks
Miners collect pending transactions from the mempool (memory pool), assemble them into a candidate block, and then repeatedly hash the block header with different nonces until they find a hash that meets the network's difficulty target. The first miner to find a valid hash broadcasts the block to the network and earns the block reward.
Block size and capacity
Each block has a maximum size limit that caps how many transactions it can include:
- Bitcoin — ~1–4 MB (with SegWit), typically 1,500–3,000 transactions
- Kaspa — blocks are intentionally small and frequent (multiple per second)
- Monero — dynamic block size that adjusts to demand
When the network is busy, transactions with higher fees get included first; low-fee transactions wait in the mempool.
