What Does "one Part" Mean When Mixing Drinks?

When mixing a single drink, one part is usually the equivalent of 1 ounce. A classic vodka martini, for example, uses six parts of vodka and one part of dry vermouth, which is the equivalent of 6 ounces of vodka and 1 ounce of dry vermouth. To make a pitcher of martinis using 1/2-cup measurements as the parts instead of ounces is the same as mixing 3 cups of vodka and 1/2 cup of dry vermouth.