Estimate cocktails per guest.
Cocktail planning works backwards from the drink count. One cocktail per guest per hour is the standard planning rate for a party where food is served, and it already builds in the fact that some guests drink more and some drink none. Each drink takes a two-ounce pour, so a 750 ml bottle at 25.4 ounces makes about twelve cocktails — the figure worth remembering. Ice is the item most often under-bought: allow a pound and a half per guest, because ice is used for shaking as well as serving and most of the shaking ice is discarded.
Cocktail Party
Cocktails = guests x hours x cocktails per hour; spirit oz = cocktails x pour size; bottles = spirit oz / bottle size, rounded up; ice lb = guests x 1.5
Quantity planning only. Serve responsibly, offer non-alcoholic alternatives and food, never serve anyone under the legal drinking age, and ensure guests have a safe way home.
About twelve at a two-ounce pour from a 750 ml bottle, or sixteen at an ounce and a half. Divide the bottle size in ounces by your pour.
A pound and a half per guest for a cocktail party. Shaking uses ice that gets thrown away, so the amount needed is roughly double what a soft-drinks party would use.