Block
A Bitcoin block is a batch of transactions that miners add to the chain about every 10 minutes, each one sealed to the block before it.
As of 15 Oct 2026, 23:05 UTC, the newest block is block 971,630.
A batch of transactions chained to the block before it. One is found about every 10 minutes by whichever miner first solves a hard puzzle. Each block carries the hash of the one before, so changing an old block would mean redoing every block after it.
What is inside a block?
An 80-byte header and a list of transactions. The header holds the hash of the previous block, a fingerprint of all the transactions (the merkle root), the time, the difficulty target and the nonce miners change while they search. The first transaction is always the coinbase, which pays the miner.
Why can't an old block be changed?
Each header contains the hash of the one before it. Change one transaction in an old block and its hash changes, which breaks the link from every block after it. Rewriting history means redoing the proof of work of all those blocks faster than the rest of the network adds new ones.
How big is a block?
A block can weigh at most 4 million weight units, about 1 million virtual bytes. In practice that is a few thousand ordinary transactions, depending on how large they are.
Sources
- Bitcoin: A Peer-to-Peer Electronic Cash System (the white paper)
- Bitcoin developer guide: block chain
Updated 10 Oct 2026
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