Block time

Block time is not a physical constant but a consensus design parameter. Under Proof of Work, as in Bitcoin, it is a statistical target of about ten minutes that emerges from mining difficulty adjustment, recalibrated every 2,016 blocks (roughly two weeks) to hold that average despite hashrate changes. Under Proof of Stake, as in Ethereum after The Merge on 15 September 2022, the time is near-deterministic: twelve-second slots grouped into epochs of 32 slots each.

Block time sets the latency of the first confirmation and, together with block size, the throughput or transactions per second. Very short times raise the orphan-block rate because network propagation cannot keep up. One nuance is worth keeping: block time is not the same as finality. Under Proof of Work confirmation is probabilistic and several blocks are awaited; in Ethereum finality is reached by epochs, around 12.8 minutes, independent of the twelve-second slot.

Bitcoin runs on a ten-minute target with difficulty readjustment every 2,016 blocks. Ethereum produces a block every twelve seconds per slot, with 32 slots per epoch. Solana shows the low-latency extreme with slots of about 400 milliseconds. It is the baseline metric for comparing networks and shapes the payment experience: how long a user waits to see a transaction confirmed.