Question 1

How many nonce values does a miner try before finding a valid block?

Accepted Answer

The number of attempts depends on the current difficulty. At Bitcoin's current difficulty, miners try quintillions of hashes before finding a valid block on average. The standard nonce field in a Bitcoin block header is 32 bits (about 4.3 billion values), which is not enough — miners also vary the coinbase transaction and timestamp to create additional nonce space (called the extra nonce).

Question 2

What happens when a valid nonce is found?

Accepted Answer

When a miner finds a nonce that produces a hash below the difficulty target, they broadcast the completed block to the network. Other nodes verify the hash independently — this verification is instant since they only need to hash the header once. If valid, the block is added to the chain, the miner receives the block reward, and all miners begin working on the next block.

Question 3

What is the extra nonce?

Accepted Answer

The extra nonce is additional data in the coinbase transaction that miners modify to expand the search space beyond the 32-bit nonce field. Since 4.3 billion nonce values are exhausted in seconds by modern ASICs, miners change the extra nonce to alter the Merkle root, effectively creating a new set of 4.3 billion nonces to try. This gives miners a practically unlimited search space.

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