What grind size should I use for pour-over?
Start in the medium range, roughly the texture of table salt or slightly coarser, and let the drawdown time tell you which way to move. Too fast and thin means finer, pooling and bitter means coarser.
Grind size for filter is a target you find by result, not by micron number, because two grinders set to the same nominal size produce different distributions. The practical anchor: a single-cup V60 with 15 g of coffee and 250 g of water should finish draining somewhere around 2:30 to 3:30 from the first pour. A larger dose takes longer, so a 30 g brew at 500 g can comfortably run to 4 minutes.
Use time plus taste together, since either alone can mislead. Fast drawdown with a thin, sour, watery cup means under-extraction and you should go finer. Slow drawdown with a bitter, drying, hollow cup means over-extraction and you should go coarser. Fast drawdown with a bitter cup is unusual and normally points at too-hot water or a very dark roast rather than grind.
Adjust by roast level too. Light roasts are dense and resist extraction, so they generally want a finer grind than the same brewer would use with a medium roast, sometimes noticeably finer. Dark roasts are brittle, they shatter into more fines and extract fast, so they usually want coarser.
Match the grind to the brewer geometry as well. A conical V60 with a large single hole drains fast and tolerates a finer grind. A flat-bottom brewer with small holes restricts flow, so a grind that works in a V60 will stall in it, and you go a step or two coarser. Immersion brewers and French press are coarser still, since contact time does the work instead of flow rate.
One quiet variable people miss: agitation. Pouring aggressively, stirring, or swirling the bed all increase extraction and speed up fines migration, which slows drawdown. If you change your pour technique and your brew suddenly stalls, do not immediately blame the grind, because you changed two things at once.