Glossary

Nonce

Plain-language definition Crypto glossary

Key takeaways

A nonce is a "number used once" that miners repeatedly change while searching for a hash that meets the network's difficulty target.
Because the right nonce is hard to find but trivial to verify, the nonce search is the actual "work" that secures a proof-of-work blockchain.
A separate kind of nonce is used on account-based chains to order each address's transactions and prevent replay.

Definition

A nonce (“number used once”) is a value that is varied to produce a different cryptographic result. In proof-of-work mining it is the number miners repeatedly change while searching for a valid block.

How it works

To mine a block, a miner hashes the block’s contents together with a nonce and checks whether the resulting hash meets the network’s difficulty target. If not, they change the nonce and try again, billions of times per second, until one produces a qualifying hash. The winning nonce is included in the block so anyone can verify the solution instantly.

Why it matters

The nonce search is the “work” in proof of work: it is hard to find but trivial to check, which is what secures the network. A separate kind of nonce is also used in account-based chains to order each address’s transactions and prevent replay.

Example

A miner that finds the right nonce earns the block reward; everyone else immediately verifies their answer and moves on.

FAQ

Frequently asked questions

What does a nonce actually do in mining?

It is the value a miner varies to change the output of the block hash. Miners try billions of nonces per second until one produces a hash that falls below the difficulty target, and that winning nonce is stored in the block so anyone can instantly verify the solution.

Why is it called a "number used once"?

The name reflects that the value is meant to be unique for a given attempt rather than reused. In mining each guess uses a different nonce, and in account-based transaction nonces each number is used once per address to keep transactions in order.

Is the mining nonce the same as a transaction nonce?

No. A mining nonce is the changing value in the proof-of-work hash search, while a transaction nonce on account-based chains is a counter that sequences an address's transactions and prevents replay. They share the name but serve different purposes.