Difficulty

Difficulty is the network's built-in measure of how much computational effort is currently required to find a valid block hash. It is expressed as a multiple of the easiest possible target, so a difficulty of 100 trillion means the network as a whole must perform roughly 100 trillion times more work than it did when the chain launched in order to produce one block.

No person or company sets difficulty: the protocol recalculates it automatically using a fixed formula tied to actual block times. On Bitcoin, every 2,016 blocks the software compares the real time it took to mine that batch against the 20,160 minute target (two weeks at 10 minutes per block). If blocks arrived faster than expected because more hash rate joined the network, difficulty rises for the next period; if blocks arrived slower, for example after unprofitable miners shut down their rigs or a region loses power, difficulty falls. Bitcoin's rules cap each adjustment at a factor of four in either direction, which stops one extreme two-week stretch from swinging difficulty too far in a single step.

Other Proof of Work chains apply the same principle on different schedules. Litecoin also retargets every 2,016 blocks but aims for 2.5 minute blocks, while Monero recalculates difficulty after every single block for tighter responsiveness. Because higher difficulty directly increases the electricity and hardware cost of producing each coin, it is one of the main variables miners track alongside the block reward and the periodic halving of that reward, both of which determine whether mining stays profitable.