Mining Difficulty
A number the network raises or lowers so blocks keep arriving at the intended average pace, whatever mining power joins or leaves.
Difficulty determines how low a block hash must be to count as valid, so doubling it halves the chance that any given guess wins. Bitcoin recalculates it every 2016 blocks by comparing how long those blocks actually took with the two-week target, with the change capped at a factor of four in either direction; other networks retarget every block using a moving average. Without this feedback loop, growing mining capacity would shorten block times and accelerate issuance, and a sudden loss of capacity would stall the chain permanently. In practice a large drop in hash rate makes blocks slower until the next adjustment lowers the requirement, which is exactly what happened when a large share of Bitcoin mining relocated between regions in 2021.
In practice
After a sharp fall in hash rate, Bitcoin blocks arrive slower than the ten-minute target until the next retarget reduces difficulty and restores the pace.
The common misunderstanding
Difficulty does not set transaction fees or make sending harder; it only controls how hard it is to find a valid block.
The figure this maps to
A number that sets how hard it is to find a valid block on a proof-of-work chain.
Limits: Difficulty is a lagging response to hash rate rather than an independent signal: it changes only at scheduled adjustments and therefore reports conditions that have already passed, which makes it unsuitable for detecting a change in mining activity quickly. The absolute value is meaningless across…