Grind size controls how fast water can extract flavor from coffee, and matching it to your brew method's contact time is arguably more important than the specific bean you buy. Water sitting in contact with grounds for a long time needs a coarser grind so it does not over-extract into bitterness, while water passing through fast needs a finer grind to extract enough flavor before it is gone.
Extra coarse, think large, chunky breadcrumb-sized particles, is used for cold brew, where grounds steep in water for 12 to 24 hours. That extremely long contact time means even a coarse grind has plenty of time to extract fully, and anything finer would turn muddy and over-extracted over that many hours. We cover the full method in our cold brew guide.
Coarse grind, similar in texture to sea salt, is the standard for a French press, where grounds steep for about four minutes before being pressed through a metal mesh filter. Too fine a grind here causes two problems at once, over-extraction from the longer contact time and sediment slipping through the mesh filter into your cup.
Medium grind, closer to regular table salt or beach sand, is the default for standard drip machines and some pour-over methods, matching a contact time of roughly four to six minutes. This is the middle of the spectrum and the grind size most pre-ground supermarket coffee is set to, since it works reasonably well across the widest range of methods even if it is not perfectly optimized for any single one.
Medium-fine grind is used for pour-over methods like a V60 or Chemex, where a paper filter and a faster pour time call for a bit more surface area than a standard drip machine needs. This is also roughly where a moka pot sits, though moka pot grind is often described slightly finer than pour-over, closer to table salt but not quite espresso-fine.
Fine grind, similar to granulated sugar, is used for espresso, where water is forced through under pressure in under 30 seconds. That short contact time needs maximum surface area to extract enough flavor, and getting this wrong is extremely obvious, too coarse and the shot runs too fast and tastes sour and thin, too fine and it runs too slow, or not at all, and comes out bitter and over-extracted. Lance Hedrick has some of the clearest video explanations of how a small grind adjustment shows up in the shot.
Extra fine, almost powder-like, is reserved for Turkish and Greek-style coffee, where the grounds are not filtered out at all but simply settle at the bottom of the cup after brewing. We walk through that method fully in our Turkish coffee guide.
If you only own one grinder and brew multiple ways, a burr grinder with adjustable settings is worth the investment over a blade grinder, since blade grinders chop unevenly and cannot reliably hit a specific, consistent size, which matters far more the finer your target grind gets. We compare the two directly in our burr vs blade grinder guide, and Perfect Daily Grind's guide to grind size, consistency and flavor covers why consistency matters as much as the setting itself.