A Bitcoin Block, What are the Blocks in Blockchain?
A Bitcoin Block

A Bitcoin Block, What are the Blocks in Blockchain?

By Thalers-r | Crypto Curious | 2 Jun 2020

A Bitcoin block is a piece of data that contains certain information. A block is one of many blocks in blockchain which are the chain links and form the Bitcoin blockchain. Approximately every 10 minutes, a new block is added to the chain. There are hundreds of thousands of blocks in the Bitcoin blockchain, actually there are 632801 blocks or in other words current block height is 632801 as of writing.

So, what is a block?

Well do not be shocked but it is a computer file. It has a minimum size of 80 bytes if there are no transactions. The more the transactions the larger the block gets. It can be as large as 1MB. It cannot exceed that. This means every Bitcoin block has a 1MB block size limit. This limit could have been 500Kb or 10MB but it is 1 megabyte because it is what Satoshi Nakamoto deemed suitable for Bitcoin.

Let’s see what a block consists of in a simple way

A Bitcoin block consists of 5 elements:


1) Magic Number:  The Magic Number of Bitcoin is 4 bytes of data. It is at the beginning of every block in the blockchain of Bitcoin and it is always F9BEB4D9. If you would like to read more about Bitcoin's Magic Number please click here.

2) Block Size: Size of the block in bytes. It occupies 4 bytes.

3) Block Header: The elements of a block header of Bitcoin shown in the picture below. For a more detailed explanation you can read this.


A Block Header formed by six elements:

  • Version number shows the current version of the Bitcoin
  • Previous Hash holds 32 bytes of space and contains hash of previous block header. The beauty in this is: block header from where the hash comes from has a previous hash too which contains the data of previous block and one before that and one before that and it goes all the way back to the Genesis Block. So, every block in the whole blockchain contains all the information of the entire history till that block. An elegant design…
  • Merkle Root root hash of all transactions’ hashes coupled up and hashes computed out of them again then again until there is only one hash left in a tree structure. This one hash is called Merkle Root. A really fascinating design, to read more about merkle trees and how they work you can click here.



  • Difficulty target is 4 bytes of data, stored as a number. It is used in mining new blocks and ensuring the time between blocks is 10 minutes.
  • Timestamp is 4 bytes of number which represents block’s date and time
  • Nonce is an arbitrary number to solve the mining puzzle.

4) Transaction count:  Number of transactions in a block. Its size varies between 1 and 9 bytes.

5) Transaction: All the transactions in that block. The number of the transactions can be as many as the total size of the related block remains under the 1 MB limit.

Thank you for reading. I hope, you enjoyed it and/or helped you somehow.
Have a nice day :)

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Statistician, crypto enthusiast, amateur photographer.

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