It depends on your brew method.
AeroPress, medium-fine
A short, flexible brew that benefits from a finer grind for balanced extraction.
Plunger (French press), coarse
A longer immersion brew that works best with a coarse grind for a clean, full-bodied cup.
Pour over (V60), medium-fine
A fast-flowing brew that benefits from a finer grind to achieve balanced extraction.
Pour over (Chemex), medium-coarse
The thick paper filter slows the brew, so a slightly coarser grind helps maintain a balanced extraction.
Automatic coffee brewer, medium
The classic middle ground, suited to the steady flow and longer brew time of drip coffee makers.
Espresso, fine
A short brew under pressure that needs a fine grind to create enough resistance for proper extraction.
Moka pot, fine
A short, pressure-driven brew that benefits from a fine grind, though not as fine as espresso.
Cold brew, extra coarse
A long 12–24 hour brew that benefits from a coarse grind for a smoother, cleaner cup.