THE SHORT ANSWER
Use fine grounds for espresso, medium-fine for many cone drippers, medium for many drip machines and medium-coarse for a French press. These are starting descriptions; your grinder, brewer and coffee decide the final setting.
Ignore the universal number
Setting 12 on one grinder does not equal setting 12 on another. Even two models from the same brand can have different ranges. Begin with the manufacturer’s guide for your equipment and keep a note of the setting, dose and brewing result.
Follow the flow and the flavour
In a dripper or espresso basket, grind size affects how water moves through the bed. Very fine grounds can slow a brew; very coarse grounds may let it race. Particle distribution and uneven flow complicate the picture, so a slow brew is evidence to investigate, not an automatic diagnosis.
Make a small tasting experiment
Brew the same coffee twice using the same dose and water. Move the grinder only a little between cups. Compare sweetness, dryness, sharpness and body once both have cooled enough to taste. Keep the better setting, then refine again. Save the extreme fine-versus-coarse experiments for small batches so your adventure does not consume the entire bag.
Change one thing, taste, and keep a short note. A recipe becomes useful when you can repeat the cup you enjoy.
Try it for yourself
Sources & further reading
Source links support the factual context. Our home recipes and tasting suggestions are identified as starting points.