Why ratios beat measures
Most classic cocktails are built around ratios — "2 : 1 : 1" tells you everything. Pick any unit (jigger, ounce, mL), and the drink scales. Doubling the batch is just doubling the unit.
Cocktail ratio calculator
Pick a classic ratio (or enter your own), set the base spirit amount, and the calculator gives every other ingredient and the batch total. Batch for a party by changing the “drinks” field.
Ingredients (relative parts)