Bitcoin Hash Rate and Mining Difficulty Explained
Hash rate is the combined computing power of Bitcoin miners, and difficulty keeps blocks about ten minutes apart. Learn how both work and what they mean.
By Christopher Cannucciari · Published
Key takeaways
- A hash is a fixed-length fingerprint of any data. Mining is a search for a block hash that falls below a target number.
- Hash rate is the number of hashes per second that all miners try together. Nobody can read it directly, so it is estimated from how fast blocks are found.
- Difficulty is how demanding that target is. Every 2,016 blocks, about two weeks, the protocol resets it so blocks keep arriving about every ten minutes.
- More hash rate does not create more bitcoin or faster blocks. It makes each block harder to win and an attack on the ledger more expensive.
- The halving leaves the difficulty rules unchanged. This article quotes no live values, and the last section says where to find them.
What is a hash?
A hash is a fixed-length string of characters that a hash function produces from any input, a bit like a fingerprint for data. Bitcoin uses a function called SHA-256, which always returns 256 bits, usually written as 64 hexadecimal characters. For block hashes, Bitcoin applies it twice to the block’s header.
Two properties matter. The same input always gives the same output, and changing a single character produces an output that looks completely unrelated. Here are the first 16 of the 64 characters from one pass of SHA-256:
| Input | Start of the hash |
|---|---|
| bitcoin | 6b88c087247aa2f0 |
| Bitcoin | b4056df6691f8dc7 |
The other property is that nobody can work backward from a hash to its input or predict what a new input will produce. The only way to find an input with a hash of a chosen kind is to try inputs one after another, which is the whole basis of mining. A miner takes a candidate block, changes a number in its header called the nonce, hashes it, checks the result and tries again. Inside a Bitcoin Mining Operation covers the machines and the money, and How Does Bitcoin Work? covers blocks.
What is hash rate?
Hash rate is the number of hashes per second that miners perform, either for one machine or for the whole network. The unit prefixes step up by a factor of 1,000: kilohash, megahash, gigahash, terahash, petahash, exahash and zettahash.
Single mining machines are usually quoted in terahashes per second. The network total is quoted in exahashes per second or higher.
No one reports the network’s hash rate, because miners do not have to disclose their machines. It is inferred instead: if blocks are found faster than the target pace at a known difficulty, more computing power must be at work. Blocks arrive at random, so a one-day estimate bounces around, and most charts show averages over several days or weeks.
What is mining difficulty?
Mining difficulty is a number describing how hard it is to find a valid block hash. A block counts only if its hash, read as a very large number, is below a target, and the lower the target, the more attempts a miner needs.
A useful picture is leading zeros: imagine asking for a hash that begins with a certain number of zeros. Each extra hexadecimal zero makes the search 16 times harder. Anyone can repeat this test: hash the text “banking-0”, then “banking-1”, and keep counting until the output starts with the required zeros.
| Leading zeros required | Average attempts needed | Attempts in this test |
|---|---|---|
| 1 | 16 | 33 |
| 2 | 256 | 301 |
| 3 | 4,096 | 3,408 |
| 4 | 65,536 | 121,208 |
| 5 | 1,048,576 | 1,862,495 |
The results wander around the average because each attempt is a fresh roll of the dice. Bitcoin’s target works the same way but is a fine-grained number, so difficulty changes smoothly and not in steps of 16. The easiest allowed setting, used at the start in 2009, is difficulty 1, and every later value is a multiple of it. As a rule of thumb, finding a block takes about the difficulty multiplied by 4.3 billion attempts, on average.
How does the difficulty adjustment work?
Every 2,016 blocks, each node recalculates the difficulty by comparing how long those blocks took with the intended two weeks, which is 2,016 blocks at ten minutes each. If the blocks came faster, the target is made harder, and if they came slower, it is made easier. One adjustment cannot move difficulty by more than a factor of four in either direction.
No one votes on this or runs it. Every node does the same arithmetic on the same public block times and rejects any block that misses the target its own calculation requires. What Is a Bitcoin Node? explains what running one involves.
Here is a made-up example. Suppose miners add so many machines that 2,016 blocks take one week instead of two. The next adjustment roughly doubles the difficulty, and blocks return to about ten minutes apart. The reverse also holds. If half of all machines switched off right after an adjustment, blocks would come about every 20 minutes, and the next adjustment would be four weeks away. Something like this followed China’s 2021 mining crackdown: blocks slowed, then difficulty fell at later adjustments and the pace recovered.
Ten minutes is an average and not a schedule. Blocks are found by chance, so some arrive within seconds and a few take over an hour.
Why does difficulty go up or down?
Difficulty follows hash rate with a delay, so it rises when miners add computing power and falls when they remove it. Newer, more efficient machines coming online push hash rate up. So do a higher bitcoin price, higher fees or cheaper electricity, which make mining more attractive and draw in more miners.
Pressure the other way comes from a lower price, rising power costs, outages or local rules, which can push the least efficient operators to switch off. Blocks then slow, and the next adjustment lowers the difficulty.
Over the long run, difficulty has tended to rise, with occasional dips. Rising difficulty does not slow transactions and does not create more bitcoin, because issuance is fixed by block count and the adjustment exists to hold the pace steady. It also says nothing about where the price is going, and this site makes no predictions.
What do hash rate and difficulty say about security?
A higher hash rate makes it more expensive to attack Bitcoin’s record of transactions. To rewrite recent blocks, an attacker would need a majority of the network’s computing power for long enough to outrun the honest miners, which means buying or renting enormous amounts of hardware and powering it.
Even then, the attacker’s power is limited. A majority could reorder recent transactions or reverse its own payments, but it could not take coins from addresses it holds no keys for, create bitcoin beyond the schedule, or force nodes to accept different rules.
Hash rate is a rough gauge of attack cost and not a guarantee. How the power is spread across mining pools matters, and so does what an attacker could gain. Proof of Work vs Proof of Stake compares this security model with the main alternative, and Bitcoin’s Energy Use: What the Debate Is Really About covers the electricity side.
What does the halving do to hash rate and difficulty?
The halving does not change the difficulty rules. It halves the subsidy, the newly issued bitcoin in each block, every 210,000 blocks, and the 2,016-block adjustment and ten-minute target stay as they were. What Is the Bitcoin Halving? lists the dates and rewards.
What can change is miners’ income. After a halving, the new-coin part of a block pays half as many bitcoin. Miners with high costs may stop, which would lower hash rate, slow blocks for a while and lead to a lower difficulty at the next adjustment. Higher prices or fees, or more efficient machines, can offset the cut, so there is no fixed outcome, and four halvings are too few to call it a rule. How Long Does It Take to Mine a Bitcoin? shows what your share of hash rate means for an expected wait.
Where can you check the current hash rate and difficulty?
Block explorers and mining-statistics sites publish these numbers, and a node you run yourself can report them too. This article gives no current values because they change daily and differ by source.
Block explorers show the present difficulty and a projection of the next adjustment. Mining-statistics sites chart hash rate and difficulty over time, typically with moving averages. A node reports the difficulty it enforces and an estimate of network hash rate.
Check the date, the averaging window and the unit, since mixing up exahashes and zettahashes is an easy error. A chart of hash rate tells you about miners and is not advice about money, so for decisions involving mining or bitcoin, talk to a qualified professional.
New to the topic? The Start Here path lists the core guides in order.
Where to go next
- Inside a Bitcoin Mining Operation: machines, pools and the economics behind hash rate.
- What Is the Bitcoin Halving?: how the block reward is cut and what stays the same.
- How Long Does It Take to Mine a Bitcoin?: what your share of hash rate means in practice.
- Bitcoin’s Energy Use: What the Debate Is Really About: the electricity behind all those hashes.
- Bitcoin Mining Pools Explained: How Miners Share the Work and the Reward: why most miners join a pool.
Frequently asked questions
What is Bitcoin's hash rate?
Hash rate is the number of hash calculations per second that all miners on the network perform together. It is a measure of the total computing power competing to add the next block. Nobody measures it directly, so it is estimated from how quickly blocks are being found.
What is Bitcoin mining difficulty?
Mining difficulty describes how hard it is to find a valid block hash. A block is valid only if its hash, read as a number, falls below a target, and difficulty is that target expressed as a multiple of the easiest one allowed. A smaller target means more attempts are needed on average.
How often does mining difficulty change?
It is recalculated every 2,016 blocks, which is about two weeks when blocks arrive every ten minutes. If the last 2,016 blocks came faster than intended the difficulty rises, and if they came slower it falls.
Does the halving change mining difficulty?
No. The halving cuts the block subsidy but leaves the difficulty rules untouched. It can change miners' income, which may lead some to switch machines on or off, and the normal difficulty adjustment then responds to whatever happens to hash rate.
Does a higher hash rate make Bitcoin more secure?
A higher hash rate makes it more expensive to rewrite recent blocks, because an attacker would need a majority of that computing power. It is a rough gauge of attack cost and not a guarantee, since factors such as how the power is spread across mining pools also matter.
