Cocktail recipes mix exact units with proportional ones. Converting them correctly matters because balance depends on ratios, while dilution depends on ice, temperature and time.
A part is a ratio
“Two parts spirit to one part citrus” can mean 2 oz to 1 oz for one drink or 200 ml to 100 ml for a batch. Choose one base measure and use it consistently. Parts do not tell you the final serving size until that base is chosen.
Fluid ounces are volume
A US fluid ounce is about 29.6 ml; the imperial fluid ounce is different. Modern cocktail books aimed at the US usually mean the US unit, but translated and older books deserve a check. A jigger marked in ounces and millilitres removes repeated mental conversion.
Dashes and barspoons need context
A dash comes from the bottle's dasher top and is not one universal laboratory volume. A barspoon also varies. Consistency within your own setup matters more than false precision; note the bottle and spoon used when refining a recipe.
Scaling changes more than multiplication
A batched drink still needs the water that shaking or stirring would have added. Citrus and other fresh ingredients may not hold for the same time as spirits. Scale the ratio first, then plan chilling and dilution rather than simply multiplying every line.
