Hashrate is the total computing power that miners point at a Proof of Work blockchain. For Bitcoin, it is the number of hash calculations the whole network attempts every second. It is one of the most quoted Bitcoin statistics and one of the most misread. This guide covers what it measures, how it is estimated and what it can and cannot tell you.
What a Hash Is
A hash function takes any data and produces a fixed-length output that looks random. Change one character of the input and the output changes completely. Bitcoin uses a function called SHA-256.
To add a block, a miner must find a block header whose hash is below a target number set by the network. There is no shortcut. Miners change a small field in the header called the nonce, hash again and repeat, trillions of times per second. The first to find a valid hash broadcasts the block and collects the block reward plus transaction fees.
This process is the Proof of Work described in the Bitcoin whitepaper. The work is hard to produce and easy for everyone else to check.
Units of Hashrate
Each attempt is one hash. Hashrate is counted in hashes per second, and each unit below is 1,000 times the one before it.
- TH/s: terahashes per second, a trillion hashes. Used for single mining machines.
- PH/s: petahashes per second. Used for mining farms.
- EH/s: exahashes per second, a quintillion hashes. Used for the whole Bitcoin network.
In 2009, Bitcoin could be mined on an ordinary computer processor. Miners moved to graphics cards and then, from 2013, to ASICs, which are chips built only for SHA-256. A modern ASIC produces hundreds of terahashes per second, and the network total has grown by many orders of magnitude since 2009.
How Hashrate Is Estimated
Nobody can count the machines directly. Miners do not report to anyone. Hashrate is inferred from two things that are public: the current difficulty and how fast blocks are being found.
If blocks arrive faster than the 10-minute average the protocol aims for, more hashing power must be at work than the difficulty assumed. If they arrive slower, there is less. Bitcoin's own software exposes this estimate through a command called getnetworkhashps, which calculates it from recent blocks.
Finding a block is a matter of luck, so block times vary a lot. A daily hashrate figure can jump 10% or more from one day to the next without any machines being switched on or off. Averages over a week or longer are much more reliable than a single day's number.
Difficulty Adjustment
Every 2,016 blocks, about two weeks, Bitcoin recalculates its difficulty. If the last 2,016 blocks took less than two weeks, difficulty rises. If they took longer, it falls. A single adjustment is limited to a factor of four in either direction.
This keeps blocks close to 10 minutes apart no matter how much hardware joins or leaves. It is also why more hashrate does not create more bitcoins. The issuance schedule stays the same, and miners simply compete harder for it. The Bitcoin developer guide on mining describes how miners and pools work with the target.
Hashrate and Security
To rewrite recent transactions, an attacker would need to out-mine the rest of the network, which in practice means controlling more than half of the hashrate. This is known as a 51% attack. The higher the total hashrate, the more hardware and electricity such an attack requires.
For Bitcoin, that cost is very large. Smaller Proof of Work coins with low hashrate are a different matter, and several have been attacked this way.
Total hashrate is not the whole picture. Most miners join pools, and a few large pools find most of the blocks. Individual miners can switch pools at any time, but pool concentration is a risk the total number does not show.
What Moves Hashrate
- Bitcoin price: a higher price makes more machines profitable to run.
- Halvings: each one cuts the block subsidy in half and squeezes miners with high costs.
- Hardware: each new generation of ASICs does more hashing per unit of electricity.
- Energy costs: electricity is the main running cost, so miners gather where power is cheap.
- Regulation: in mid-2021, China banned mining. The network's estimated hashrate fell by roughly half within weeks and recovered by the end of that year as machines moved to other countries.
What Hashrate Does Not Tell You
Hashrate is not a price forecast. It tends to follow price with a delay, because miners add machines after mining becomes more profitable. A new record in hashrate says miners are investing. It does not say the price will rise.
A falling hashrate does not mean the network is broken either. Blocks slow down for a while, the difficulty adjusts and the network carries on. The 2021 drop is the clearest example.
Common Mistakes
- Reacting to a one-day spike or drop that is only statistical noise
- Comparing hashrate between coins that use different hash functions, which is not meaningful
- Assuming home mining is profitable without calculating electricity cost against current difficulty
- Treating hashrate as a reason to buy or sell
Nothing in this article is financial advice.
Key Hashrate Facts
- Hash function: SHA-256
- Target block time: 10 minutes
- Difficulty adjustment: every 2,016 blocks, about two weeks
- Network unit: exahashes per second (EH/s)
- Measurement: an estimate from block times and difficulty, not a direct count
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