Glossary

Proof of Work

Plain-language definition Crypto glossary

Key takeaways

Proof of Work is a consensus mechanism in which miners compete to solve a computationally difficult puzzle, and the first to find a valid solution adds the next block and collects the block reward.
Miners repeatedly hash a block's data with a changing nonce until the result falls below a network target, which takes enormous numbers of guesses to find but is instant to verify.
The real electricity and hardware cost of mining is what secures the chain, because rewriting history would require out-computing the honest majority.

Definition

Proof of work is a consensus mechanism where network participants (miners) compete to solve a computationally intensive puzzle in order to add the next block to a blockchain. Solving the puzzle is deliberately difficult and resource-intensive, while verifying a solution is quick, which lets the rest of the network confirm a block was earned fairly.

Why it matters

Proof of work secures the network by making it expensive to attack: an attacker would need more computing power than the honest network combined to rewrite transaction history, and that computing power costs real electricity and hardware. The trade-off, widely discussed, is significant energy consumption compared with alternative mechanisms like proof of stake.

Example

Bitcoin is the original and largest proof-of-work blockchain. See live data on our Bitcoin page.

FAQ

Frequently asked questions

Why does Proof of Work use so much electricity?

Finding a valid solution requires miners to make enormous numbers of hash guesses, which consumes real electricity and hardware. That cost is not waste from a security standpoint; it is what makes attacking the chain prohibitively expensive.

How does the network keep block times steady?

The protocol automatically adjusts the difficulty of the puzzle based on how much mining power is online. If more miners join, difficulty rises so blocks still arrive at a roughly steady pace, and it falls if mining power drops.

What stops someone from rewriting the blockchain?

To rewrite history an attacker would have to redo the work and out-compute the honest majority of mining power, which is prohibitively expensive. This economic cost of mining is precisely what secures a Proof of Work chain.