Proof of work (PoW)
Also called: PoW
Definition
Proof of work (PoW) is a consensus mechanism in which miners use computing power to solve a puzzle, and the first to find a valid answer earns the right to add the next block and collect the reward.
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How Proof of work works
Miners repeatedly hash a candidate block with a changing number until the result falls below a target set by the network. There is no shortcut; the only way is to try trillions of guesses. Finding a valid hash is hard, but anyone can check it instantly, which is what makes the system work.
Because adding blocks costs real electricity and hardware, attacking a PoW chain is expensive. To rewrite history, an attacker would need more than half of the network's hash rate and would have to keep spending energy to stay ahead. Bitcoin is the best-known PoW network; Litecoin, Dogecoin and Bitcoin Cash also use it.
The network adjusts difficulty automatically. On Bitcoin, difficulty changes every 2,016 blocks so blocks keep coming about every 10 minutes no matter how many miners join. Critics point to PoW's energy use, while supporters argue that the cost is exactly what secures the ledger. Ethereum used PoW until it switched to proof of stake in September 2022.
Example
Suppose the Bitcoin network runs at 600 exahashes per second and a small mining farm contributes 6 exahashes per second, or 1 percent. With about 144 blocks per day, the farm can expect to win around 1.44 blocks daily on average. At 3.125 BTC per block, that is roughly 4.5 BTC per day before fees and electricity costs, though actual daily results vary with luck.
Common mistakes
- Thinking miners solve useful math problems; the puzzle is pure guessing designed to cost energy.
- Assuming more miners means faster blocks, when difficulty adjusts to keep timing steady.
- Believing a home computer can still mine Bitcoin profitably; specialised ASIC machines dominate.
Learn and practise
FAQ
What is the difference between proof of work and proof of stake?
Proof of work secures the chain with computing power and electricity. Proof of stake secures it with coins locked up as collateral by validators.
Why does Bitcoin use proof of work?
It makes attacks costly in real-world resources and lets anyone verify which chain has the most work behind it, without trusting a central party.
Is Ethereum still proof of work?
No. Ethereum switched to proof of stake in September 2022 with the Merge.