What is a Bitcoin block?

A Bitcoin block contains a set of data that holds all the information necessary to verify transaction and link the block back to its previous block in the chain.

The constituent parts of a block can be seen in the table below.

The block size is simply the size of the block in bytes – this varies mainly depending on the number of transactions.

The block data is shown in the table below:

The block header is the list of meta-data about the block – a full explanation can be seen in our guide – What is a block header in Bitcoin? – the block header is an 80 byte field. The next pieces of information are the number of transactions in the block and the transactions themselves.

A transaction is usually above 250 bytes depending on its type – multisignature transactions use a lot more space due to the required conditions on spending – you can see more about the different transaction types here. The average block contains about 500 transactions – which equates to just less than one transaction per second.

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