Different methods of brewing and different styles of brewing equipment demand different sizes of coffee ground. The normal categorisations are FINE, MEDIUM and COARSE. The general rule is “the finer the grind, the quicker the infusion”. So smaller grounds do not need to be in the water as long as larger grounds.
GENERAL GUIDELINES
Brewing Method Recommended Grind
Ibriq (Turkish Coffee Pot) Powdered
Espresso Very Fine
Drip Filter Medium
Plunger Pot Medium
Cafetiere Medium
That is how you get the right grind for your coffee.
Source: Excerpts from Coffee by Jane Pettigrew