## Definition

**Mining difficulty** is a numerical value that controls how hard it is to find a hash that satisfies Bitcoin's [proof of work](/glossary/proof-of-work) requirement, first described in the [Bitcoin whitepaper](https://bitcoin.org/bitcoin.pdf). It rises as more hash power joins the network and falls as miners leave. The difficulty value is expressed as a multiple of the easiest possible difficulty (difficulty 1), and it directly determines the target hash threshold that every valid block must beat.

## How It Works

Bitcoin recalculates difficulty every **2,016 blocks** — roughly every two weeks. The protocol compares actual block production to the [target of one block every 10 minutes](https://en.bitcoin.it/wiki/Difficulty):

- **If blocks came faster than 10 min on average** → difficulty increases
- **If blocks came slower than 10 min on average** → difficulty decreases

Adjustments are capped at **4× up or down** per period to prevent extreme swings.

## Why It Matters

The difficulty adjustment is what makes Bitcoin's monetary policy predictable. No matter how much mining hardware comes online, blocks (and therefore new bitcoin issuance) arrive at the same average pace.

It also enforces a kind of equilibrium:

- Rising prices → more miners → higher difficulty → marginal miners squeezed out
- Falling prices → miners leave → difficulty drops → remaining miners earn more per unit of hash

## Difficulty vs. Target

The **target** is the actual hash threshold a [block header](/glossary/block-header) must beat. Difficulty is just a human-friendly way to express it: a difficulty of 1 corresponds to the highest possible target; higher difficulty = lower target = harder to find a valid hash. In block headers, this target is stored in the compact [nBits format](https://developer.bitcoin.org/reference/block_chain.html#target-nbits).

## Related Terms

- [What is Bitcoin Mining?](/glossary/what-is-bitcoin-mining)
- [Proof of Work](/glossary/proof-of-work)
- [Hash Rate](/glossary/hash-rate)