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What is hashrate?
Hashrate is the number of guesses per second that miners make while searching for a valid Bitcoin block. It measures the computing power working on the network, and is usually written in terahashes per second (TH/s) or exahashes per second (EH/s).
What it means for you
Hashrate is what an attacker has to outpace: rewriting confirmed blocks means redoing their work faster than the honest miners, so each confirmation on a high-hashrate chain is harder to undo. Sudden changes in hashrate also make blocks arrive faster or slower until difficulty catches up.
How it works
Each guess hashes an 80-byte block header with a different nonce; a block is valid when the hash does not exceed the target. A header's 4-byte nonce covers only about 4 gigahashes, so mining hardware needs fresh work many times a second. The whitepaper calls proof of work one-CPU-one-vote: the chain with the most work wins, so changing a past block means redoing it and every block after it, then overtaking the honest chain. Difficulty is set by a moving average so that blocks keep a steady pace whatever the total hashrate.
Sources: Bitcoin vocabulary (bitcoin.org), Bitcoin Developer Guide: Mining, Bitcoin: A Peer-to-Peer Electronic Cash System (whitepaper) · checked 4 October 2026
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