Nonce
mining · proof-of-work
A nonce is a value miners vary in a block header while searching for a hash that satisfies proof-of-work difficulty.
- Also known as
- number used once
"Nonce" is short for "number used once," but a block-header nonce is simply a 32-bit search field and does not need to be globally unique. Miners vary it and other mutable candidate-block data, repeatedly hashing the header until an output is below the network's current target. That header contains valid proof of work if the rest of the block is also valid.
Because the 32-bit nonce space can be exhausted quickly, miners also vary other fields (like extraNonce in the coinbase transaction or block timestamp within allowed drift) to expand the search space.
The nonce is not secret or inherently unpredictable. The hash function and difficulty target make each distinct header attempt have a small probability of success, so producing valid blocks requires work on average. Network security also depends on hash-rate distribution, node validation, incentives, and participants' response to competing chains.
Related terms
Proof of Work (PoW)
→A consensus mechanism that makes block production require verifiable computational work.
mining · blockchain · consensus
Block
→A batch of valid transactions added to a blockchain, linked to the previous block by a cryptographic hash.
mining · blockchain · security
Transaction
→A serialized state transition that a blockchain can validate, relay, and include in a block.
blockchain · technical
Mempool
→A node's local set of unconfirmed transactions accepted for possible relay and block inclusion.
blockchain · node