Definition
Mining variance is the statistical randomness baked into proof-of-work. Because each hash is an independent lottery ticket with the same tiny odds, the time between blocks, and between shares, is unpredictable in the short run even when your hashrate is constant. Variance is why two identical miners can have very different results over a day or a week, and why it exists at every scale of mining.
Variance and pooling
The practical effect of variance shrinks as you combine more hashrate. Pooling thousands of miners averages out individual swings: roughly speaking, the variance experienced by a pool participant is the solo variance divided across the pool, producing far steadier income. This is the core reason most miners join a pool rather than chase rare solo wins. A single small open-source board mining solo might statistically wait centuries for a block, while pooling turns that into frequent, predictable micro-payouts.
Reading variance correctly
Operators get into trouble when they mistake variance for a problem. A pool going several rounds without a block, or a solo machine producing nothing for months, can be entirely normal randomness rather than a fault. The signal to watch is long-run average performance against expectation, not any single hour or day. Over enough blocks, results converge on the statistical mean.
When variance is measured against a pool's expected share count it is reported as pool luck, and it is the central trade-off in solo mining versus pooled mining.
In Simple Terms
Mining variance is the statistical randomness baked into proof-of-work. Because each hash is an independent lottery ticket with the same tiny odds, the time between…